Modular fabrication systems and methods

ABSTRACT

The present invention relates to an article fabrication system having a plurality of material deposition tools containing one or more materials useful in fabricating the article, and a material deposition device having a tool interface for receiving one of the material deposition tools. A system controller is operably connected to the material deposition device to control operation of the material deposition device. Also disclosed is a method of fabricating an article using the system of the invention and a method of fabricating a living three-dimensional structure.

This application is a continuation of U.S. patent application Ser. No.16/883,217, filed May 26, 2020, which is a continuation of U.S. patentapplication Ser. No. 16/528,593, filed Jul. 31, 2019, now U.S. Pat. No.10,695,466, issued Jun. 30, 2020, which is a continuation of U.S. patentapplication Ser. No. 16/023,153, filed Jun. 29, 2018, now U.S. Pat. No.10,406,262, issued Sep. 10, 2019, which is a continuation of U.S. patentapplication Ser. No. 14/965,317, filed Dec. 10, 2015, now U.S. patentSer. No. 10/034,964, issued Jul. 31, 2018, which is a continuation ofU.S. patent application Ser. No. 14/504,375, filed Oct. 1, 2014, nowU.S. Pat. No. 9,242,031, which is a continuation of U.S. patentapplication Ser. No. 14/146,179, filed Jan. 2, 2014, now U.S. Pat. No.8,877,112, which is a continuation of U.S. patent application Ser. No.13/052,787, filed Mar. 21, 2011, now U.S. Pat. No. 8,636,938, which is acontinuation of U.S. patent application Ser. No. 11/201,057, filed Aug.10, 2005, now U.S. Pat. No. 7,939,003, which claims the priority benefitof U.S. Provisional Patent Application Ser. No. 60/704,299, filed Aug.1, 2005, and U.S. Provisional Patent Application Ser. No. 60/600,529,filed Aug. 11, 2004, all of which are hereby incorporated by referencein their entirety.

FIELD OF THE INVENTION

The present invention relates generally to an article fabricationsystem, a method of fabricating an article, and a method of fabricatinga living three-dimensional structure.

BACKGROUND OF THE INVENTION

Solid freeform fabrication (“SFF”) is the name given to a class ofmanufacturing methods which allow the fabrication of three-dimensionalstructures directly from computer-aided design (“CAD”) data. SFFprocesses are generally additive, in that material is selectivelydeposited to construct the product rather than removed from a block orbillet. Most SFF processes are also layered, meaning that a geometricaldescription of the product to be produced is cut by a set of parallelsurfaces (planar or curved), and the intersections of the product andeach surface—referred to as slices or layers—are fabricatedsequentially. Together, these two properties mean that SFF processes aresubject to very different constraints than traditional materialremoval-based manufacturing. Nearly arbitrary product geometries areachievable, no tooling is required, mating parts and fully assembledmechanisms can be fabricated in a single step, and multiple materialscan be combined, allowing functionally graded material properties. Newfeatures, parts, and even assembled components can be “grown” directlyon already completed objects, suggesting the possibility of using SFFfor the repair and physical adaptation of existing products. On theother hand, a deposition process must be developed and tuned for eachmaterial, geometry is limited by the ability of the deposited materialto support itself and by the (often poor) resolution and accuracy of theprocess, and multiple material and process interactions must beunderstood.

SFF has traditionally focused on printing passive mechanical parts orproducts in a single material, and the emphasis of research has been ondeveloping new deposition processes (U.S. Pat. No. 5,121,329 to Crump;U.S. Pat. No. 5,134,569 to Masters; U.S. Pat. No. 5,204,055 to Sachs et.al.; and U.S. Pat. No. 5,126,529 to Weiss et. al.), on improving thequality, resolution, and surface finish of fabricated products, and onbroadening the range of single materials which can be employed by agiven SFF process, including biocompatible polymers and otherbiomaterials (Pfister et al., “Biofunctional Rapid Prototyping forTissue-engineering Applications: 3D Bioplotting Versus 3D Printing,”Journal of Polymer Science Part A: Polymer Chemistry 42:624-638 (2004);Landers et al., “Desktop Manufacturing of Complex Objects, Prototypesand Biomedical Scaffolds by Means of Computer-assisted Design Combinedwith Computer-guided 3D Plotting of Polymers and Reactive Oligomers,”Macromolecular Materials and Engineering 282:17-21 (2000)), and livingcells (Roth et al., “Inkjet Printing for High-throughput CellPatterning,” Biomaterials 25:3707-3715 (2004)). These improvements haveallowed freeform fabrication to become a viable means of manufacturingfinished functional parts, rather than only prototypes.

More recently, the greater utility of freeform fabricated productshaving multiple materials has been recognized, prompting reexaminationand novel research into processes which can fabricate using multiplematerials (U.S. Pat. No. 5,260,009 to Penn), and which can therebyproduce complex articles with a variety of functionality, includingfunctionally graded materials (Ouyang et al., “Rapid Prototyping andCharacterization of a WC—(NiSiB Alloy) Ceramet/Tool Steel FunctionallyGraded Material (FGM) Synthesized by Laser Cladding,” Columbus, Ohio,USA: TMS—Miner. Metals & Mater. Soc. (2002); Smurov et al.,“Laser-assisted Direct Manufacturing of Functionally Graded 3D Objectsby Coaxial Powder Injection,” Proceedings of the SPIE—The InternationalSociety for Optical Engineering 5399:27 (2004)), electronics, MEMS(Fuller et al., “Ink-jet Printed Nanoparticle MicroelectromechanicalSystems,” Journal of Microelectromechanical Systems 11:54-60 (2002)),living tissue constructs (Mironov et al., “Organ Printing:Computer-aided Jet-based 3D Tissue Engineering,” Trends in Biotechnology21:157-161 (2003)), and compositions of living and nonliving materials(Sun et al., “Multinozzle Biopolymer Deposition for Tissue EngineeringApplication,” 6^(th) International Conference on Tissue Engineering,Orlando, Fla. (Oct. 10-13, 2003); International Patent Application No.PCT/US2004/015316 to Sun et al.; and U.S. Pat. No. 6,905,738 toRingeisen et al.). All of these systems still depend upon a small fixedset of deposition process technologies, and are therefore limited to thematerials which can be adapted to those processes, by the effects ofthose particular processes on the materials, and by the fabricationrates and resolutions of those processes. In particular, the system ofU.S. Pat. No. 6,905,738 to Ringeisen et al., requires that for everymaterial to be deposited, a two material system be developed comprisingthe material to be transferred, and a compatible matrix material whichis vaporized by the laser in order to propel the transfer material tothe substrate. In addition, this system has only demonstratedfabrication of thin films of materials—its ability to deposit manylayers of materials is not well established. The system and method ofSun et al., “Multinozzle Biopolymer Deposition for Tissue EngineeringApplication,” 6^(th) International Conference on Tissue Engineering,Orlando, Fla. (Oct. 10-13, 2003) and International Patent ApplicationNo. PCT/US2004/015316 to Sun et al., is limited to a fixed set of fourdeposition processes and requires that the alginate materials bedeposited into a bath of liquid crosslinking agent—a limitation itshares with the work of Pfister et al., “Biofunctional Rapid Prototypingfor Tissue-engineering Applications: 3D Bioplotting Versus 3D Printing,”Journal of Polymer Science Part A: Polymer Chemistry 42:624-638 (2004)and Landers et al., “Desktop Manufacturing of Complex Objects,Prototypes and Biomedical Scaffolds by Means of Computer-assisted DesignCombined with Computer-guided 3D Plotting of Polymers and ReactiveOligomers,” Macromolecular Materials and Engineering 282:17-21 (2000).In addition, none of these systems explicitly measures the propertiesof, and monitors and controls the conditions experienced by thefabrication materials, the fabrication substrate, and the article underconstruction before, during, and/or after fabrication as an intrinsicpart of the fabrication process and manufacturing plan. The fabricationprocess is thus limited to the spatial control of material placement onrelatively simple, passive substrates. Temporal control of the evolutionof material properties is therefore not possible, and complex substrateswhose state must be controlled and monitored continuously are notreadily accommodated. Fabricating into or onto substrates, such asliving organisms or devices which must remain in operation continuously,is problematic.

A major challenge in orthopaedic tissue engineering is the generation ofseeded implants with structures that mimic native tissue, both in termsof anatomic geometries and intratissue cell distributions. Previousstudies have demonstrated that techniques such as injection molding(Chang et al., “Injection Molding of Chondrocyte/Alginate Constructs inthe Shape of Facial Implants,” J. Biomed. Mat. Res. 55:503-511 (2001))and casting (Hung et al., “Anatomically Shaped Osteochondral Constructsfor Articular Cartilage Repair,” J. Biomech. 36:1853-1864 (2003)) ofhydrogels can generate cartilage tissue in complex geometries. Otherstudies have investigated methods to reproduce regional variations inarticular cartilage constructs by depositing multiple layers ofchondrocytes (Klein et al., “Tissue Engineering of Stratified ArticularCartilage from Chondrocyte Subpopulations,” Osteoarthritis Cartilage11:595-602 (2003)) or chondrocyte-seeded gels (Kim et al., “ExperimentalModel for Cartilage Tissue Engineering to Regenerate the ZonalOrganization of Articular Cartilage,” Osteoarthritis Cartilage11:653-664 (2003)). However, there remains no viable strategy forrapidly producing implants with correct anatomic geometries and celldistributions. Recently, advances in SFF techniques have enabled thedeposition of multilayered structures composed of multiple chemicallyactive materials (Malone et al., “Freeform Fabrication of 3D Zinc-AirBatteries and Functional Electro-Mechanical Assemblies,” RapidPrototyping Journal 10:58-69 (2004)). Applicants believe that thistechnology has the potential to be adapted to the fabrication of livingtissue under conditions that preserve cell viability.

The present invention is directed at overcoming disadvantages of priorart approaches and satisfying the need to establish a robust andreliable SFF system and method.

SUMMARY OF THE INVENTION

One aspect of the present invention relates to an article fabricationsystem. The system has a plurality of material deposition toolscontaining one or more materials useful in fabricating the article. Thesystem has a material deposition device having a tool interface forreceiving the material deposition tools, the tool interface of thematerial deposition device being movable relative to a substrate todispense material from the material deposition tool to the substrate. Asystem controller is operably connected to the material depositiondevice to control operation of the material deposition device.

Another aspect of the present invention relates to a method offabricating an article. This method involves providing theabove-described article fabrication system. Material is dispensed fromthe material deposition tools, when mounted on the tool interface of thematerial deposition device, in amounts and at positions on the substratein response to instructions from the system controller, whereby anarticle is fabricated on the substrate.

A further aspect of the present invention relates to a method offabricating a living three-dimensional structure. This method involvesproviding a data set representing a living three-dimensional structureto be fabricated. One or more compositions including a compositionhaving a hydrogel with seeded cells is provided. The one or morecompositions are dispensed in a pattern in accordance with the data setsuitable to fabricate the living three-dimensional structure.

Yet another aspect of the present invention relates to an articlefabrication system. The system has a material deposition tool containingone or more materials useful in fabricating the article. The system hasa material deposition device having a tool interface for receiving thematerial deposition tool, the tool interface of the material depositiondevice being movable relative to a substrate to dispense material fromthe material deposition tool to the substrate. The system has anenclosure defining a receptacle for enclosing the substrate in aconfined environment segregated from other components of the system andcapable of receiving material dispensed from the material depositiontool. A system controller is operably connected to the materialdeposition device to control operation of the material depositiondevice.

Yet a further aspect of the present invention relates to an articlefabrication system. The system has a material deposition tool containingone or more materials useful in fabricating the article. The system hasa material deposition device having a tool interface for receiving saidmaterial deposition tool, the tool interface of the material depositiondevice being movable relative to a substrate to dispense material fromthe material deposition tool to the substrate. The system has one ormore sensors positioned to detect non-geometric properties of materialdispensed to the substrate. A system controller is operably connected tothe sensors to control detection of material properties and to thematerial deposition device to control the material deposition device.

The present invention relates to an article fabrication system havingmultiple interchangeable material deposition tools and one or moremodules capable of receiving material dispensed from material depositiontools. The deposition tools may contain interchangeable cartridgescontaining materials useful in fabricating the article. The tools and/orthe cartridges may also contain apparatus for monitoring andconditioning the material for deposition. The substrate modules areuseful in fabricating the article, and may also contain apparatus formonitoring and conditioning the deposited materials.

The system may also have a device to automatically switch tools andtheir cartridges and substrate modules, or these may be fixed in thesystem. A system controller is operably connected to the material tools,cartridges, substrate modules, transfer devices, and positioningsystems. The system has provision for monitoring and controlling theenvironmental conditions under which fabrication takes place, formonitoring and correcting fabrication errors during the course offabrication, and for monitoring and controlling the properties of thearticle being fabricated during the course of fabrication. The combinedcapabilities of the system, the deposition tools, and the substratemodules allow monitoring and control of the conditions experienced byall of the materials and by the article being fabricated, before,during, and/or after the fabrication process. This extends the freeformfabrication process to include controlled evolution of materialproperties as well as controlled deposition of multiple materials,allowing not just geometric, but spatio-temporal control over theproperties of the composite article being fabricated. These extendedcapabilities are especially important when fabricating integratedsystems comprising multiple active materials, such as electrochemicaldevices and living tissue constructs. This is also the case whendepositing constructs into sensitive substrates, such as livingorganisms or sensing devices, the health and function of which must bemaintained throughout the fabrication process.

The present invention's modular system architecture and multi-levelcontrol scheme give it distinct advantages over other systems. Themodular system architecture enables the system of the present inventionto adapt to high throughput applications, in which material changes andsubstrate changes must be efficient and, in some cases, in whichautomation would be beneficial. The modular design also enables thesystem to adapt to a broad range of applications. For example, the samegeneral system design could be used for in vitro as well as in vivofabrication.

The multi-level sensing, actuation, control, and intelligence enablesthe system to log and/or control the spatio-temporal state of numerousproperties of both materials and articles being fabricated prior,during, and after fabrication (for example, from the start of thefabrication process through incubation). These material and articleproperties include but are not limited to temperature, humidity, light,vibration, pressure, mechanical loading, and shape. Spatio-temporalcontrol of numerous properties is important when fabricating integratedsystems with active materials such as electromechanical devices,self-assembling structures, and living tissue constructs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a fabrication system in accordance withthe present invention.

FIG. 2 is a perspective view of a material deposition device and thetool rack of the system in accordance with the present invention inwhich the tool rack is connected to the material deposition device.

FIG. 3 is a front view of a material deposition device of a system inaccordance with the present invention without a material deposition toolattached at the tool interface.

FIG. 4 is a front view of a material deposition tool in accordance withthe present invention, which is a cartridge holding tool capable ofreceiving a modular material cartridge.

FIG. 5 is a front view of a material deposition device in accordancewith the present invention fitted at a tool interface with a cartridgeholding tool capable of receiving a modular material cartridge.

FIG. 6 is a front view of a cartridge holding tool in which a modularmaterial cartridge carrying a syringe is positioned in the cartridgechamber.

FIG. 7 is a front view of a material deposition device of a system inaccordance with the present invention fitted at the tool interface witha cartridge holding tool in which a modular material cartridge carryinga syringe is positioned in the cartridge chamber.

FIGS. 8A-D are perspective views of a cartridge holding tool andmaterial modular syringe cartridge that fits into the cartridge holdingtool. FIGS. 8A-B illustrate perspective, exploded views of the parts ofa syringe which fit into the syringe cartridge. FIG. 8C illustrates aperspective, exploded view of how the syringe fits into the syringecartridge. FIG. 8D illustrates a perspective view of the cartridgeholding tool fitted with the syringe cartridge.

FIG. 9 is a perspective view of a transfer device in accordance with thepresent invention.

FIG. 10 is a perspective view of a fabrication system in accordance withthe present invention in which the transfer device is in contact with amaterial deposition tool located on a tool rack. Also shown is theelectronic wiring of a fabrication system that connects to an externalcomputer.

FIG. 11 is a perspective view of a fabrication system in accordance withthe present invention in which a transfer device is replacing a materialcartridge in a cartridge socket of a material deposition tool connectedto a tool interface.

FIG. 12 is a back view of a material deposition device in accordancewith the present invention showing a sensor attached to the back of thetool interface. The sensor detects properties of the substrate, of thearticle being fabricated, and of the materials being deposited.

FIG. 13 is a perspective view of a tip calibration sensor positioned ona substrate of a material deposition device. The tip calibration sensorenables the system controller to be aware of the precise location of areference point on the tool or tools attached to the tool interfacerelative to the tool interface.

FIG. 14A is a front view of a module in accordance with the presentinvention which is attachable to the substrate. A plan view (FIG. 14B)and a side view (FIG. 14C) of the substrate module are also shown.

FIG. 15 is a perspective view of a module in accordance with the presentinvention depicting a receptacle into which material from a materialdeposition device is dispensed and examples of fixture points,interfaces, and sensing and actuation ports which may be included in themodule.

FIG. 16 is a perspective view of a module in accordance with the presentinvention in which a receptacle is enclosed.

FIG. 17 is an exploded perspective view of a module in accordance withthe present invention.

FIG. 18 is a perspective view of a fabrication system in accordance withthe present invention in which a module is attached to a substrate.

FIG. 19 is a perspective view of a fabrication system in accordance withthe present invention in which a module having an enclosed receptacle isattached to a substrate.

FIGS. 20A-B are photographs showing the results of viability tests inwhich both live (FIG. 20A) and dead (FIG. 20B) cells were detected inprinted gels.

FIG. 21A is a stereolithography (“STL”) image of a bovine meniscusgenerated by a CT scan. FIG. 21B is a photograph of the printedmeniscus-shaped gel using the fabrication system and method of thepresent invention.

FIG. 22 is a photograph of a 1-millimeter thick, autoclavable, clearplastic bag used to enclose the substrate in a sterile environment.

FIG. 23 is a photograph of a plastic bag containing a printed samplewhich has been transferred to a sterilized hood for removal of afabricated article.

FIGS. 24A-L are photographs of printed gels using the fabrication systemmethod of the present invention compared to images generated by CTscans.

FIG. 25A-B are photographs of microscope views during viability testsusing fluorescence microscopy filtered to illuminate living cells (FIG.25A) and filtered to illuminate dead cells (FIG. 25B).

FIG. 26A is a CAD model image generated from a CT scan of ameniscus-shaped piece of cartilage used in fabricating the article shownin FIG. 26B.

FIG. 26B is a photograph of a fabricated article produced by afabrication system in accordance with the present invention.

FIG. 27A is a CAD model image generated from a CT scan of ameniscus-shaped piece of cartilage used in fabricating the article shownin FIG. 27B.

FIG. 27B is a photograph of a fabricated article produced by afabrication system in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

One aspect of the present invention relates to an article fabricationsystem. The system has a plurality of material deposition toolscontaining one or more materials useful in fabricating the article. Thesystem has a material deposition device having a tool interface forreceiving the material deposition tools, the tool interface of thematerial deposition device being movable relative to a substrate todispense material from the material deposition tool to the substrate. Asystem controller is operably connected to the material depositiondevice to control operation of the material deposition device.

Another aspect of the present invention relates to an articlefabrication system. The system has a material deposition tool containingone or more materials useful in fabricating the article. The system hasa material deposition device having a tool interface for receiving thematerial deposition tool, the tool interface of the material depositiondevice being movable relative to a substrate to dispense material fromthe material deposition tool to the substrate. The system has anenclosure defining a receptacle for enclosing the substrate in aconfined environment segregated from other components of the system andcapable of receiving material dispensed from the material depositiontool. A system controller is operably connected to the materialdeposition device to control operation of the material depositiondevice.

A further aspect of the present invention relates to an articlefabrication system. The system has a material deposition tool containingone or more materials useful in fabricating the article. The system hasa material deposition device having a tool interface for receiving saidmaterial deposition tool, the tool interface of the material depositiondevice being movable relative to a substrate to dispense material fromthe material deposition tool to the substrate. The system has one ormore sensors positioned to detect non-geometric properties of materialdispensed to the substrate. A system controller is operably connected tothe sensors to control detection of material properties and to thematerial deposition device to control the material deposition device.

FIG. 1 is a perspective view of one embodiment of the system of thepresent invention. In the particular embodiment shown in FIG. 1 , toolrack 4 is connected to material deposition device 2. Located nearmaterial deposition device 2 and tool rack 4 is transfer device 100,which is capable of making contact with material deposition tool 18 andmoving material deposition tools 18 between material deposition device 2and tool rack 4.

Material deposition device 2 and tool rack 4 are again illustrated inperspective in FIG. 2 . As shown, machine base 6 is the generalsupporting structure of material deposition device 2. Machine base 6preferably has horizontal surface 90 which may rest on the ground or ona flat surface, such as the top of a bench or a table, and two verticalsurfaces 92A-B connected to horizontal surface 90. In a preferredembodiment, machine base 6 is a large, precision granite structure,although other materials may be used in the construction of machine base6 so long as the material is capable of dissipating vibration from thehigh acceleration motions that material deposition device 2 is capableof.

Positioning system 8 is preferably a machine driven X-Y coordinategantry supported by machine base 6. Positioning system 8 has two X-axisstages, including first X-axis stage 10A and second X-axis stage 10B,preferably constructed of commercially available ballscrew stages.X-axis stages 10A-B rest on, and are attached to, vertical walls 92A-Bof machine base 6. Positioning system 8 is preferably constructed of acommercially available ballscrew stage identical to X-axis stages 10A-B.Y-axis stage 12 is fixed, at opposite ends and perpendicular to, firstX-axis stage 10A and second X-axis stage 10B and spans horizontalsurface 90.

Movement at positioning system 8 occurs as Y-axis stage 12 moves backand forth along X-axis stages 10A-B. This movement is driven by motors40A-B which, in a preferred embodiment, are high-performance brushlessDC motors with optical encoders for displacement feedback. However, anymotor which is capable of producing relatively high acceleration, goodvelocity regulation, and positioning accuracy may be used to operate themovement of positioning system 8. In operation, motor 40A drives one endof Y-axis stage 12 along X-axis stage 10A while motor 40B simultaneouslydrives the other end of y-axis stage 12 along X-axis stage 10B.

Another moving component of positioning system 8 is tool interface 20,which resides on Y-axis stage 12 and moves back and forth along Y-axisstage 12. Tool interface 20 is capable of receiving a materialdeposition tool, such as material deposition tool 18 illustrated in FIG.2 . As discussed in greater detail below, material deposition tool 18may receive material cartridges, such as material cartridge 26. Movementof tool interface 20 along Y-axis stage 12 is driven by motor 42, whichis preferably a motor similar to, or identical to, motors 40A-B. Withtool interface 20 being capable of moving back and forth along Y-axisstage 12 and Y-axis stage 12 being capable of moving back and forthalong X-axis stages 10A-B, positioning system 8 is capable of movingtool interface 20 in virtually any direction on a horizontal plane abovehorizontal surface 90.

Above horizontal surface 90 of machine base 6 and below positioningsystem 8 is substrate 16. Substrate 16 is a build surface upon whichmaterial from material deposition tool 18 is deposited. In a preferredembodiment, substrate 16 is equipped with calibration device 44, whichmay be fixed anywhere on substrate 16, but is preferably fixed to anouter edge or corner of substrate 16. Calibration device 44 is describedin greater detail below. Substrate 16 is preferably constructed of aprecision-ground aluminum plate, but may be constructed of any materialcapable of ensuring planarity. Substrate 16 rests on support structure34, which holds substrate 16 in a horizontal position or, alternatively,may be adjusted to change the orientation (i.e., angle) of the surfaceplane of substrate 16 relative to positioning system 8. Supportstructure 34 is preferably of rigid construction.

In the particular embodiment illustrated in FIG. 2 , support structure34 is connected to Z-axis stage 14. Z-axis stage 14 is preferably acommercially available ballscrew stage, identical to X-axis stages 10A-Band Y-axis stage 12. Support structure 34 moves along Z-axis stage 14 ina vertical direction either towards or away from positioning system 8,thereby adjusting the vertical distance of substrate 16 relative to thematerial deposition tool (e.g., material deposition tool 18) connectedto tool interface 20 of positioning system 8.

In operation, material deposition device 2 fabricates a product aspositioning system 8 moves material deposition tool 18 in a pathwayalong substrate 16 and material deposition tool 18 deposits materialonto substrate 16 along the pathway. Typically, fabrication of a productis carried out by layer-wise deposition of the material. This standardplanar layered deposition approach to material deposition device 2enables the system to deposit materials from material deposition tool 18in a manner which optimizes the properties of the deposited materialrelative to the specified performance metrics for the product beingfabricated—including alignment of deposited material fibers alongprimary stress axes to improve mechanical performance, depositingpolymer materials in a manner which increases the degree of molecularalignment, and improving e.g., electrical or mechanical properties.

Alternative embodiments of material deposition device 2 may be designedto permit a less massive machine base to be used. For example, a cableand pulley arrangement could be used to create a Cartesian gantry robotin which the motors remain stationary (mounted on the machine base),thereby reducing the moving mass of the system and the reaction forces.This in turn would allow the use of a smaller, lighter machine basewithout compromising stability and precision. Alternative embodimentsmay make use of other means of moving the positioning system components,including linear electromagnetic motors, pneumatics, or hydraulics.

Alternative embodiments of material deposition device 2 can also makeuse of other positioning systems including, but not limited to,articulated robotic arms for the positioning and traversing of thematerial deposition tools and/or the positioning of the substrate. Thiswould permit the material deposition device to make use of non-planardeposition paths (3-D curves) and more complex manipulation of objectsbeing fabricated. This would also provide more freedom for themanufacturing planning components of the system to arrive at plans whichmore closely match the specifications of the desired product, which mayinclude the ability to achieve 3-D curvilinear optimization of fiber ormolecular alignment in deposited materials.

Further illustrated in FIG. 2 is tool rack 4 which, in the particularembodiment shown, is connected to material deposition device 2. In analternative embodiment, tool rack 4 may be located in proximity tomaterial deposition device 2 rather than being connected. Tool rack 4 isequipped with tool mounts, such as tool mount 28, which are capable ofreceiving a variety of material deposition tools, represented by mountedtool 30 and described in further detail below. A preferred tool mount oftool rack 4 is illustrated as tool mount 28, which has fluid/gas andelectrical connectors 36 and mechanical connectors 38. Fluid/gas andelectrical connectors 36 and mechanical connectors 38 allow tool rack 4to be in electrical, fluid/gas, and/or mechanical communication withtools stored on tool rack 4. Tool rack 4 may also be equipped withcartridge holding devices 32 that are capable of receiving individualmaterial cartridges 26. Tool rack 4 may also be equipped with substratemodule holding devices that are capable of receiving individual orgroupings of substrate modules. Substrate module holding devices mayinclude electronic, mechanical, and/or auxiliary material interfaceswhich permit communication between any embedded intelligence and controlin the substrate modules and the tool rack and hence the systemcontroller. These interfaces may also provide utilities and auxiliarymaterials which may be used for the monitoring and control of the stateof the substrate module and its contents.

In a preferred embodiment, tool rack 4 is designed to provide utilityservices to material deposition tools and material cartridges which arestored on it, and to provide communication between the materialdeposition tools and the system controller. Particular services include,without limitation, power, data communication, commands, fluids, andcompressed gas. Data communication can take place between the materialdeposition tools and material cartridges stored on tool rack 4 and thesystem controller to enable the real-time status of materials andmaterial deposition tools to be controlled and/or monitored while theyare not in use. Data communication further allows the status to be usedduring manufacturing planning and allows the inventory to be managed.For example, requests for additional material can be made to a user ifthe system finds that tool rack 4 does not contain sufficient quantityof a material required in the current manufacturing task. The datacommunication also allows the system controller and/or user toreprogram, query, monitor, and/or control any embedded intelligence,sensors, and/or actuators in the material deposition tools or materialcartridges. This can include updating the identity and/or status ofmaterials contained in a tool or cartridge, and updating the internalcontrol parameters of a material cartridge and/or a material depositiontool. These features of tool rack 4 make it possible to use materialsprepared further in advance than would otherwise be possible, since theycan be kept in favorable conditions for preservation by the cartridgeuntil use. They also enable a greater level of automation, and moreefficient use of materials than is otherwise possible because thematerials can be automatically readied for use at the appropriate time,and possibly returned to storage conditions automatically by the system.Chemical reactions, cellular reproduction and metabolism, and othermaterial properties can be monitored and controlled in materialsawaiting use, enabling the controller evolution of material propertiesto be an integral part of the manufacturing plan.

Turning to the illustration in FIG. 3 , tool interface 20 is equippedwith tool interface mount 92, which is capable of receiving a materialdeposition tool. Tool interface mount 92 is a standardized toolinterface to accommodate a plurality of material deposition tools. In apreferred embodiment, tool interface mount 92 is a commerciallyavailable robotic tool changer that provides for a rigid, precise, andrepeatable automatic mounting and unmounting of material depositiontools. Preferably, tool interface mount 92 has electrical connectors,fluid/gas connectors, and mechanical connectors (e.g., a pneumaticconnection) capable of establishing electrical, fluid/gas, andmechanical communication with a connected material deposition tool.Thus, when a material deposition tool is connected to tool interfacemount 92, electrical, fluid/gas, and mechanical communication may beestablished between tool interface 20 (and the system controller and anyfluid, gas, electrical, and mechanical utilities available in thesystem) and the connected material deposition tool.

A unique feature of the system of the present invention is that ratherthan being dedicated to a single manufacturing process technology and toone or two materials, this system makes use of multiple deposition (andother manufacturing, testing, and measurement process) technologies, andan essentially unlimited number of materials. This is achieved byencapsulating a given manufacturing technology in a modular “tool”(referred to as a material deposition tool) which is manipulated by thematerial deposition device (i.e., positioning system 8) during thecourse of manufacturing, measuring, or testing an object. Tools may havesignificant onboard sensing, actuation and computational resources inorder to monitor and control their own performance, and/or the state ofthe material that they are employing, as well as for communicating stateinformation and control parameters with the system controller.

Material deposition tools useful in the system of the present invention(i.e., for positioning on tool interface mount 92) include, withoutlimitation, various commercially available material deposition tools andmaterial deposition tools described herein.

In one embodiment, one of the material deposition tools is afusible-material extrusion tool for depositing thermally liquefiedplastics, low melting-point metals, and other fusible materials.Fusible-material extrusion tools are commercially available. Typically,this type of tool employs motor-driven pinch-rollers to force feedstockmaterial (in the form of a wire) into a heated portion of the tool andout of a constricted orifice (nozzle). The heated portion of the toolsoftens or melts the feedstock, permitting it to be pushed out of thenozzle as a fine stream of liquid or semi-liquid material. Nozzles arereplaceable, and nozzle orifice diameters may be smaller than 0.010 ofan inch.

Various modifications may be made to commercially availablefusible-material extrusion tools for use with the system of the presentinvention. These design modifications may include a temperature sensorpositioned directly in the nozzle, immediately proximate to the pointwhere the material is deposited to control the extrusion temperature ofthe deposited material. In addition, the pinch-rollers may be modifiedto have a tooth shape which is optimized for minimal damage to thefeedstock and maximum buckling strength of the feedstock as it is driveninto the tool, allowing the feedstock to be driven with more force intothe heater block and out of the nozzle. This modification permits fasterextrusion rates and/or finer resolution (via narrower nozzles). Inanother modification, the body of the tool may be made of organicpolymers to reduce the mass of the tool and thereby improve theperformance of the positioning system while the tool is in use by thesystem. Also, the tool may be equipped with a muffler surrounding thefeed stock material through which fluid or compressed gas may becirculated in order to actively cool the feedstock material afterpassing through the pinch roller and before reaching the heater block.This would also increase the buckling strength of the feedstock materialand would allow for faster extrusion and/or higher resolution.

In another embodiment, one of the material deposition tools used in thesystem of the present invention is an ink-jet tool. Ink-jet tools, inparticular, and, more generally, any tool can be used to depositmultiple reactants into the same spatial location in order to effect achemical reaction on a very local scale. The very small volumesachievable with ink-jet droplets (e.g. picoliters) are especially wellsuited to this. Ink-jet droplets of multiple reactants jetted into thesame location will react very quickly, permitting the local controlchemical reactions within deposited material, allowing very small scalestructuring of chemical activity and resultant material properties.Reactant concentrations can be varied by relative numbers of drops ofeach type of reactant deposited at a give point. This can allowreactions fast enough that reactants do not have time to move (e.g.,drip or flow) or evaporate or degrade before the reaction takes place.An ink-jet tool is capable of depositing multiple (e.g., four) materialssimultaneously without material changes. An important benefit ofink-jetting for material deposition is high resolution (100 μm×100 nmdisk-shaped deposit per droplet), especially when working with materialswhose functionality depends on their being produced in thin films (e.g.,semiconducting polymers, dielectrics, separator materials for batteries,electroding materials for actuators). The very small volume of droplets(picoliter) achievable with ink-jetting allows deposition of materialonto non-planar surfaces. The very small droplets not only dry extremelyquickly, but the small gravitational force they experience allows themto adhere to sloped and curved surfaces without the flowing that largerdrops would experience. This is exceedingly valuable when fabricatingarticles with complex, non-planar geometries containing non-horizontaland/or non-planar laminae or other structures. The high resolution andpoint-by-point deposition of material permits structures (such as linearfeatures whose material varies with length, or multi-material lattices)to be practically realized, making the products of an ink-jet toolcomplementary to those that can be achieved by a stream-type depositiontool such as a syringe tool (described below).

In a further embodiment, one of the material deposition tools is anelectrospinning tool. An electrospinning tool uses an electricalpotential difference between the material, generally a fluid, containedin the tool, and the substrate to draw the material out of the tool inextremely fine streams. This potential difference can be achieved byplacing one electrode in contact with the fluid within the tool, andanother electrode on the substrate (if it is conductive) or on aperforated electrically conductive plate placed between the tool and thesubstrate. A central hole in the latter plate is arranged concentricallywith the outlet or nozzle of the tool so that the fluid stream may passdirectly through and continue to be deposited on the substrate. Volatileliquid components of the material may evaporate from the stream ofmaterial because of electrostatic charging and self-repulsion andbecause of the very large surface area to volume ratio of the stream.The material which arrives at the substrate may thus be a dry thread ofmaterial with a diameter of nanometers. Adjusting the materialcomposition, the spacing between the substrate and the tool, and theelectrical potential can allow control of the liquid content anddiameter of the deposited material. This type of tool permits theproduction of nanoscale structures, including highly aligned polymermolecules. Such a tool provides the system with the ability to embedmaterials structured at the nanometer scale into macroscopic objectsbeing fabricated.

In another embodiment, one of the material deposition tools may be a“pick and place” robot tool. A “pick and place” robot tool is devicewhich can hold, reorient, and accurately place an object onto asubstrate. The materials dispensed by a “pick and place” robot tool mayinclude integrated circuits, passive electrical components, electricalmotors, batteries, and any other discrete solid objects withcharacteristic dimensions ranging from 100 micrometers to 10centimeters. For example, a “pick and place” robot tool might placeintegrated circuit components onto conductive pads and conductive tracesdeposited by other material deposition tools in the course offabricating an article. Still, other material deposition tools mightthen encapsulate the circuit components and conductive pads and tracesin an insulating material to produce an article with embeddedexogenously manufactured components.

In other embodiments, the material deposition tools may include, but notbe limited to: thermal spray deposition tools, vapor deposition tools,and laser forward transfer deposition tools.

A thermal spray deposition tool is a device in which a solid materialpowder is entrained in a gas stream which is directed at the substrate.The stream is passed through a heat source prior to arriving at thesubstrate such that the powder particles are melted and deposited astiny molten drops.

A vapor deposition tool employs a stream of gas to entrain vaporevaporated from a solid or liquid material contained in a heatedreservoir. Within the tool, the gas stream flows past or through thereservoir, entrains the vapor, and is directed out of an orifice towardthe substrate. When the substrate is below the condensation temperatureof the vapor, the vapor will condense onto the substrate. The rate andmorphology of deposited material can be regulated by varying thereservoir temperature, the gas stream velocity, and temperature, thesubstrate temperature, the orifice diameter, and the distance fromorifice to substrate.

A laser forward transfer deposition tool employs a pulsed laser totransfer material from a source substrate to a receiving substrate. Thesource substrate is located between the laser and the receivingsubstrate. The source substrate generally consists of a lasertransparent medium, such as a strip, tape, or disk of glass, fusedsilica, or polymer. The lower surface of the source substrate—that whichfaces the receiving substrate—is coated with a thin layer (e.g. 0.1-1000micrometers) of the material to be deposited. A pulse from the laser isdirected at the source substrate, passes through the transparent medium,and liberates a small quantity of the material attached to the sourcesubstrate medium. The momentum imparted to the material in the course ofliberation carries it toward the receiving substrate, where it isdeposited. After each laser pulse, the relative position of the sourcesubstrate and the laser are changed so that a region of the sourcesubstrate which has not received a pulse, and hence retains its fullcoating of material to be deposited, is placed in the path between thelaser and the desired point of deposition on the receiving substrate.

The system may also include material modification tools which areintended to modify the properties and/or geometry of material after ithas been deposited by a material deposition tool. Material modificationtools include, but are not limited to, lasers, infrared lamps,ultraviolet lamps, cutting tools, milling tools, drills, temperaturecontrolled jets of gases and/or fluids and/or gas or fluid entrainedpowders. In addition, any material deposition tool may also beintegrated with and/or mounted simultaneously with other materialdeposition tools, and/or material modification tools, and/or materialsensing apparatus. These combination tools and combinations of toolsallow the deposition and/or modification and/or measurement of one ormore deposited materials in very rapid succession. This enhances thespatiotemporal control of the system over the materials being deposited.

In yet another embodiment, one of the material deposition tools is acartridge holding tool capable of receiving a modular materialcartridge. FIG. 4 illustrates a preferred embodiment of materialdeposition tool 18, which is a cartridge holding tool equipped withcartridge socket 48 for receiving a modular material cartridge. As shownin detail in FIG. 4 , cartridge socket 48 has mechanical interfaces 52that hold a material cartridge in cartridge socket 48 and/or embeddedintelligence in the material deposition tool and/or the systemcontroller. Electronic and fluid/gas interfaces 54 establish electroniccommunication between the material cartridge placed in cartridge socket48 and the system controller and provide fluid/gas flows to the materialcartridge which may be used by the system controller and/or embeddedintelligence in the tool and/or in the cartridge to monitor and controlthe state of the cartridge, and/or the material or materials containedin the cartridge. This enhances the ability of the overall system toachieve spatiotemporal control of the evolution of material propertiesbefore, during, and after fabrication of an article. Fluid/gas flows mayalso be used in a supporting role for fabrication by being routedthrough the cartridge and directed downward toward the substrate. Thisallows the creation of a highly localized controlled environment at thepoint of material deposition e.g. with an inert gas flow to preventchemical reactions.

In a preferred embodiment, material deposition tools of the presentinvention are operably connected to the system controller, whether theyare attached to the tool interface or not.

In the particular embodiment shown in FIG. 4 , material deposition tool18 is equipped with a volumetrically controlled dispensing system havinglinear motor 56 which provides up and down force to linear shaft 50,thus driving the dispensing of material from material deposition tool18. As described in greater detail below, motor 56 is controlled by asystem controller. Linear shaft 50 has load cell 60 and electromagnet58. Load cell 60 and electromagnet 58 are placed in linear shaft 50 toprovide control to the deposition of material from a material cartridgelocated in cartridge socket 48 via sensor communication with the systemcontroller. The load cell allows the system controller and/or anyintelligence and control embedded within the tool and/or within thecartridge to monitor and/or regulate the pressure being applied by themotor via the plunger and piston to the material within the syringe.This may be done in order to achieve a desired flow of material from thecartridge. The electromagnet allows the system controller to selectivelyengage or release a mechanical connection between the motor and theplunger. According to the command of the system controller, when theelectromagnet is energized, this allows the plunger to remain engaged tothe motor regardless of whether the motor is moving upward or downward.When, according to the command of the system controller, theelectromagnet is not energized, the cartridge may be easily removed fromthe cartridge socket, and replaced. In a preferred embodiment, theunderside surface of electromagnet 58 is equipped with a contact sensorwhich monitors contact between electromagnet 58 and a syringe from amaterial cartridge and relays the information to the system controller.

FIG. 5 shows the material deposition tool of FIG. 4 attached to toolinterface 20 of material deposition device 2 of the system of thepresent invention.

FIG. 6 illustrates a material deposition tool, which is a cartridgeholding tool, loaded with material cartridge 26 in cartridge socket 48.Cartridge 26 holds syringe 66 that contains material to be depositedthrough syringe needle 68. Plunger 62 is inserted into syringe 66 atopening 64 and provides the force by which material exits syringe needle68. Plunger disk 80 at the top of plunger 62 is, in a preferredembodiment, a magnetically permeable steel disk capable of forming amagnetic connection with electromagnet 58. The magnetic connectionallows material flow from cartridge 26 to be controlled by linear motor56 of material deposition tool 18.

FIG. 7 shows the material deposition tool of FIG. 6 attached to toolinterface 20 of material deposition device 2 of the system of thepresent invention.

A detailed illustration of how a preferred syringe cartridge isassembled and loaded into a cartridge holding tool is illustrated inFIGS. 8A-D. FIG. 8A shows the various component parts of a syringe thatfits into syringe cartridge 26. These parts include syringe 66 withopening 64 at the top, syringe needle 68 which is connected to thebottom of syringe 66, and piston 70, which connects to plunger 62 (FIG.8B). Syringe 66 and piston 70 are preferably disposable, whereas plunger62 is preferably reusable.

To prepare the syringe for loading into cartridge 26, syringe 66 isfilled with material, typically by pumping material in via Luer-lock tip82 of syringe 66. This minimizes the amount of trapped air in syringe66, which improves the ability of the system to control the dispensingof the material. Syringe needle 68 is then mounted on syringe 66.

A syringe loaded with material is inserted into an opening in materialcartridge 26, as illustrated in FIG. 8C. As shown in FIG. 8D, materialcartridge 26 is then inserted into cartridge socket 48 of materialdeposition tool 18. In this position, electromagnet 58 is brought intomagnetic contact with plunger disk 80. Once material deposition tool 18is loaded with syringe cartridge 26 it may be loaded onto tool rack 4 oronto tool interface 20 of positioning system 8.

In a preferred embodiment, syringe cartridge 26 is equipped with activeelements that can monitor and control the state of the material insyringe 66 residing in syringe cartridge 26 and can communicate thisinformation to the system controller, or be programmed or controlled bythe system controller or user, via cartridge electronic interfaces 54.Syringe cartridge 26 may also contain auxiliary material interfaces 74,which mate to auxiliary material interfaces in cartridge socket 48 ofcartridge holding tool 18. These interfaces allow syringe cartridge 26to be supplied with auxiliary materials such as fluids, gases, orpowders which may be used within the cartridge to monitor and/or controlthe state of the material contained in cartridge 26, or be directed viaor by the cartridge downward onto the substrate and/or along the streamof material which is being deposited. In the latter case, theseauxiliary materials may be used to control the evolution of materialproperties after the material has been deposited. For example, heatedair may be used to accelerate evaporation of volatile materials, vacuummay be used to draw away undesirable fumes or byproducts, inert orreactive gases may be delivered to the point of material deposition toprevent or promote reactions. This communication will be routed throughelectronic interfaces in cartridge socket 48, or wirelessly communicateddirectly to the system controller and/or cartridge holding tool 18 whensyringe cartridge 26 is mounted in cartridge socket 48 of cartridgeholding tool 18, or through tool rack 4 when syringe cartridge 26 ispositioned on tool mount 28 of tool rack 4 and is waiting to be loadedinto cartridge holding tool 18 for use. In either case, syringecartridge 26 will be informed of what type of material it is loaded withand syringe cartridge 26 will begin to monitor and control the materialstate. The status information will be communicated to the systemcontroller so that accurate material data can be used in manufacturingplanning and material deposition control.

When cartridge holding tool 18 is mounted on tool interface 20 and isnot yet holding a material cartridge, an appropriate cartridge can betaken from cartridge holding device 32 of storage rack 4 and insertedinto cartridge socket 48 of cartridge holding tool 18 either by transferdevice 100 or by a user. Linear motor 56 will then move downward untilelectromagnet 58 detects contact with plunger disk 80. Electromagnet 58is energized, locking the syringe plunger disk to the linear motorshaft.

To dispense material from syringe cartridge 26 onto substrate 16, thesystem controller commands positioning system 8 to move materialdeposition tool 18 so that syringe needle 68 traces out the appropriatecurvilinear paths, while simultaneously commanding material depositiontool 18 to dispense material.

The fact that material cartridges may contain active components,computational hardware, and communication ability provides foradditional modes of control over the deposition of materials frommaterial deposition device 18, as well as allowing control of the stateof the material while it resides within a cartridge. It also permits theuse of a wider variety of materials than would otherwise be amenable todeposition. Cartridges may contain magnetic stirring or a vibrationalstirring apparatus which can be used to maintain homogeneity inmaterials (e.g. multi-phase slurries, emulsions, dispersions) thatotherwise would separate or settle, causing clogging of the tool orundesirable dispensing properties. Heating and cooling devices withinsyringe cartridge 26 may be used to manage viscosity of materials and topromote or prevent chemical or biological activity. In this way,materials can be maintained within syringe cartridge 26 in one statewhich is desirable for one set of reasons, then allowed to evolve into adifferent state after deposition. Given that the entire system of thepresent invention may reside in an enclosure (described below) whichallows environmental control—humidity, temperature, gas mix, lighting,sterility—sophisticated control over the trajectories of many materialparameters through time can be achieved, even as the material isdeposited in precisely controlled geometry.

It is possible to use the control that the active cartridge and theenclosure environment provides over the material state before, during,and after the deposition process to perform feedback control ofparameters of the deposited material other than geometry—enabling asteering of the manufacturing process toward a final product which moreclosely matches that desired. This can include such parameters as color,reflectivity, sterility, (biological) viability, mechanical properties,reactivity, odor, etc., provided that some means of detecting theseparameters can be provided to the system. This means may consist of ahuman expert and/or an appropriate automatic sensor mounted on thematerial deposition tool or embodied as a separate modular sensing tool,for sequential use. Appropriate sensors include, without limitation, CCDcameras with machine vision software, “electronic nose,” mechanicalprobes with force instrumentation, and fluorescence CCD microscopes withmachine vision software.

An alternative to sensing of these properties via a tool or sensormounted on tool interface 20 (or material deposition tool 18) is todeposit the materials directly onto a sensing apparatus, or to embed thesensing apparatus within the material as it is being deposited. Thesesubstrate or embeddable sensors include, without limitation, biochipsensors for detection of biological products and monitoring and controlof living cells and tissues, temperature sensors, semiconductor chemicalsensors, strain gauges, pressure sensors, and many others.

Because most of the material deposition tools which are used with thesystem of the present invention deposit materials through an orifice ofsome kind, there is the frequent occurrence of residual materialaccumulating around the orifice, nozzle, tip, etc. Maintaining precisecontrol of the deposition process, desired segregation of materials, andavoiding clogging and damage to tools and objects being fabricated, allrequire that the tools be cleaned periodically to remove this residualmaterial. Several approaches may be used in the system to achieve thiscleaning automatically. For tools with robust tips or nozzles andstubborn material accumulations, a wire brush, rubber scraper blade,solvent-saturated sponge, or a combination of these may be employed,namely by having positioning system 8 drive material deposition tool 18to a point on substrate 16 where these devices are mounted, then rubbingthe tip of material deposition tool 18 (or syringe cartridge 26) againstthem automatically. For more delicate tool tips, such as fine gaugeneedles, a solvent bath and/or a gas jet may be used in an analogousfashion to wash or blow material away. Because the various materialdeposition tools used in the system may span all of these needs, ingeneral, several tip cleaning devices will be positioned at the edge ofthe substrate.

Turning to FIG. 9 , in one embodiment, transfer of material depositiontools and/or substrate modules and/or material cartridges to and fromthe tool rack and/or other storage locations and the material depositiondevice is carried out by transfer device 100. In a preferred embodiment,transfer device 100 is a six-axis robotic arm. Transfer device 100 ispositioned on base 102 and extends from base 102 by various sectionsconnected by axes. In particular, section 104 is connected at base 102by axis 116, which permits section 104 to swivel axially relative tobase 102. Section 104 is connected to section 106 by axis 110, whichallows pivotal motion of section 106 relative to section 104. Likewise,section 108 pivots relative to section 106 at axis 112. Section 108 isconnected to tool grip 114 at connection 118. Connection 118 permitstool grip 114 to have three ranges of motion relative to section 108.These ranges of motion include a side to side horizontal range ofmotion, a vertical up and down motion, and an axial swivel motion. Inthe illustration of FIG. 9 , tool grip 114 is connected to materialcartridge 26. In other embodiments, the transfer device may be aconveyer belt, carousel, or human operator.

Transfer device 100 makes it possible to automatically change materialdeposition tools during the course of manufacturing a product. Thisgreatly expands the range of products that the system of the presentinvention can produce relative to a traditional freeform fabricationsystem and further allows for upgradeability and customization of thesystem and its product space, with new or specialized technologies formanufacturing, testing, and measuring products easily incorporated asnew or additional tools. Transfer device 100 may also be equipped withvarious sensors and feedback controls which communicate with the systemcontroller.

Operation of the system of the present invention is controlled by asystem controller operably connected to the material deposition deviceand the transfer device. In addition, the system controller may also beconnected to the tool rack and directly to the material depositiontools. FIG. 10 illustrates the system of the present invention withelectrical connections to system controller 104, which is an externalcomputer. Electrical line 106 extends from computer 104 and provides anelectrical connection between the system controller (i.e., externalcomputer 104) and various motors and sensors that operate the system ofthe present invention. In particular, electrical line 110A provides anelectrical connection from external computer 104 to controller/amplifier108 which, in a preferred embodiment, is a “smart amplifier.”Controller/amplifier 108 is electrically connected to transfer device100 by electrical line 110B. Movement of transfer device 100 iscontrolled by controller/amplifier 108 and external computer 104. Theseelectrical connections allow placement of a material deposition toolonto tool interface mount 92 and removal of a material deposition toolfrom tool interface mount 92 by transfer device 100 (see FIG. 11 ).

Also shown in FIG. 10 are the electrical connections between motors thatdrive positioning system 8 and external computer 104. Electrical lines116 and 112 provide electrical connection between motors 40A-B,respectively. Likewise, motors 42 and 46 are connected to externalcomputer 104 via electrical lines 120 and 114, respectively. Electricalline 118 provides an electrical connection between external computer 104and material deposition tool 18. Typically, the electrical connectionbetween the material deposition tool and external computer 104 involvescontrolling the dispensing of material from material deposition tool 18,but may also provide communication between the system controller and anyembedded intelligence, and/or actuators, and/or sensors positioned onmaterial deposition tool 18 and/or on syringe cartridge 26, and/or onany material modification tools also present in the system, which aredescribed in greater detail below. Electrical connections may also bemade between tool interface 20 and external computer 104.

In a preferred embodiment, electrical lines 112, 114, 116, 118, and 120are connected to amplifiers 124A-E, respectively, to provide additionalpower to perform mechanical operations.

Electrical connection is also preferably made between tool rack 4 andexternal computer 104 via electrical lines 122A-D which are furtherpreferably powered by amplifiers 126A-D, respectively. These electricalconnections receive information from tool rack 4 and relay it back toexternal computer 104.

Fabrication of a product using the system of the present invention iscarried out as material is deposited from material deposition tool 18 ina pattern on substrate 16. The pattern is established by the systemcontroller, which operates according to an electronic data file so thatchanges to the product only require changes to the design data of thesystem controller. In its basic operation, transfer device 100,according to a manufacturing plan programmed into the system controller,takes a specified tool from tool rack 4 and connects it to toolinterface 20. Tool interface 20 then communicates with materialdeposition tool 18 and configures it for use. Material deposition device2 then performs some steps in the manufacturing plan, e.g. depositingsome material in a designated pattern along substrate 16. Transferdevice 100 then retrieves material deposition tool 18 from toolinterface 20 and returns it to tool rack 4.

System controller 104 is operated by fabrication system software thatautomatically converts design data into a manufacturing plan. Thefabrication system software automates the majority of operations of thesystem of the present invention, permitting the designer's intent to beconverted into a realized product with a minimum of labor andprerequisite specialized knowledge about the materials being used (i.e.deposited). System controller 104 is designed to store data about systemperformance and to improve the system automatically by updating data andmodels which it uses for manufacturing planning, manufacturingsimulation, manufacturing plan execution, and operation control.

The main components of the system software of system controller 104 arethe manufacturing planning, operation control,materials/tools/substrates database, and design database. Themanufacturing planning software is responsible for converting thedesigner's intent, via the product description data, into an executableplan for producing the design. In the simplest implementation, thesystem expects the product description data to be the geometry of theproduct, with contiguous subregions of geometry (called “chunks”)labeled with the material which the designer desires for that subregion,and the tool used to deposit that material. For each chunk of geometry,the materials/tools/substrates database is queried by the planningsoftware for specifications of the material deposits that the requestedmaterial/tool combination can provide. These specifications include thegeometry of the “atomic” deposits of material that this combination canproduce. When the material deposition tool is an ink-jet tool, theatomic deposit is a deposit caused by a single drop of material from thetool. For other material deposition tools, such as a syringe tool and afusible material extrusion tool, the atomic deposit may be curvilinearwith some minimum length and some nominal cross-section dimensions.Still other atomic deposit types are possible with other materialdeposition tools, and many tools are capable of producing individualdeposits of various sizes and shapes. The simplest manufacturingplanning implementation does not take advantage of this. The essentialaspect of the atomic deposit is that it can be combined into largerdeposits by contiguous placement without producing undesirable loss ofproperties in the large deposit relative to those of the atomic deposit.The chunk geometry is decomposed into a union of geometric solids whoseform is dictated by the atomic deposit. Positions (and possibly paths)in 3-dimensional space are stored for these to be later used to specifythe paths and/or coordinates (referred to as the “set of paths,” or“toolpaths”) for material deposition to be performed by the system. Whendecomposition has been performed for all chunks in the design, the fullset of data describing these decompositions is automatically sorted tosatisfy a multiple objective optimization of the manufacturing process.This sorted set of paths (with associated tool and material labels andcoordinates) constitutes a manufacturing plan which is executable by thesystem control software and system hardware.

In the simplest approach, the sorting of paths will arrange thetoolpaths by vertical (Z-axis) coordinate and paths with the samevertical coordinate will be grouped by material/tool combination. Moresophisticated optimizations take into account more detailed informationabout the materials, tools, performance of the system itself, and knowndesign rules (e.g. from the design database) for certain aspects of thedesign. More sophisticated optimizations can also involve optimizing theshape and directionality of material deposition paths to achieve desiredproperties in the finished products. This can include optimizingmechanical properties such as tensile strength along primary stressaxes, or possibly even along 3-dimensional curves through an objectbeing fabricated. This type of final material property optimizationthrough path optimization can also be used to provide preferential axesfor tissue growth when working with living biological materials.Information to drive these optimizations can be extracted from thematerials/tools/substrates and design databases, from real-time andhistorical performance data that the system maintains about itself, andfrom a simulation of the manufacturing process. This latter methodbecomes more crucial as designs, material behavior, and materialinteractions become more complex, and specifications for the finishedproduct become more stringent. The simulation may make use of models ofmaterial evolution over time and in response to environmental conditionswhich are stored in the materials/tools/substrates database, models ofsystem operation and performance, and may perform physical simulationsof a candidate manufacturing process for a given design (includingfinite element models, or other physics-based modeling). In this way,the system can make predictions about the quality and/or performance ofa final product that might result from a given manufacturing plan, whichcan then be used for automated searching for manufacturing plans whichsatisfy the objective functions supplied by a user in the designspecifications for the object to be produced. The simulation, in aninteractive mode, can permit a designer to explore the effect ofalternative designs on the complexity of the manufacturing process. Thesimulation of the manufacturing process also plays an essential role forerror recovery/correction during a manufacturing process. Errorrecovery/correction is important because producing complex objects withnovel or experimental materials is costly and time consuming. Further,if the system does not detect and recover from errors during themanufacturing process, the errors will—by the very nature of the SFFprocess—be buried within the object being produced and be difficult orimpossible to diagnose and repair. The manufacturing simulation allowsthe system, at any step in the manufacturing process, to compare thestate (geometry and other automatically detectable properties) of thesimulation to the state of the real object being produced as measured by3-D scanning (or other) sensors. Discrepancies can be remedied bygenerating modifications to the manufacturing plan which replace orcircumvent the error—these too can be explored in simulation, and theeffect of the errors and the modifications to the manufacturing planscan be used to update predictions of the quality and performance of thefinal product.

The manufacturing planning software can include special purpose dataconversion capabilities to assist the designer in conveying design datato the system. This can include automatic conversion of computedtomography and magnetic resonance imaging data into manufacturing plangeometry data, or automatic conversion of point cloud data resultingfrom non-contact scanning directly into manufacturing plan geometrydata.

Another element of the system controller of the present invention isoperation control, which includes all of the feedback control,self-testing, data-collection software required to operate the systemhardware and execute a manufacturing plan produced by the manufacturingplanning software, including: (i) low-level control software for toolsand material cartridges which may be executed by computational hardwarewithin the tools and cartridges themselves; (ii) the feedback controllaws which operate the environmental controls within the systemenclosure; (iii) the motion control software that commands thepositioning systems and coordinates positioning system control with tooldeposition control; (iv) control and path planning for the transferdevice used for tool and material changes; and (v) scanning sensorcontrol, data collection, and data conversion.

The materials/tools/substrates database component of the systemcontroller is used to store information about the properties ofmaterials used in fabrication, the types and shapes of deposits ofmaterial that can be made by a given deposition tool, specializedparameters for controlling deposition tools to achieve each type ofdeposit, selection and parameters for controlling material modificationtools to achieve a desired modification of material properties,parameters for controlling substrate modules in order to achieve adesired trajectory of materials properties evolution, materialinteractions with other materials, and other information. The materialproperties information may be in the form of a complex material model,which can include time evolution of the material properties in responseto conditions. This type of information may be used in many ways inmanufacturing planning and manufacturing simulation, including: (i)generating plans for the control of material substrate modules andenclosure environmental conditions to guide the evolution of materialproperties before, during, and after deposition (e.g. cellularreproduction rates, chemical reaction rates, etc.); (ii) identifyingcomplications in a manufacturing plan, e.g. where adjacent materialsmight be reactive, where a liquid might need to be deposited only aftera solid boundary has been constructed to contain it; and (iii)identifying how long manufacturing plan steps must be spaced by in orderto allow deposited materials to solidify, react, etc.

The information in the database is compiled from a variety of sources.First, the embedded intelligence, sensing, and communications inmaterial deposition tools and cartridges obtains real-time informationon quantity and status of materials loaded into the system for use inthe current manufacturing plan, and health and operational status of thetools. Second, chemical or materials data references and research obtaingeneral chemical and materials properties data and dynamic propertiesmodels. Third, manual calibration by operators or machine learningalgorithms within the system (Malone et al., “Application of MachineLearning Methods to the Open-Loop Control of a Freeform FabricationSystem,” Proceedings of the 15th Solid Freeform Fabrication Symposium,Austin Tex., August 2004, pp. 377-388, which is hereby incorporated byreference in its entirety) retrieve tool control parameters required togenerate a given material deposit geometry.

The design database is a repository of subunits of manufacturing plansand design rules of thumb that have been demonstrated to be successful,as well as complete designs and manufacturing plans for usefulfunctional modules that are likely to be desirable inclusions into otherdesigns. Maintaining this database is important, because no practicalmanufacturing simulation will be able to predict all issues of concernduring manufacturing. The successful designs, rules, tricks, and modulescapture much of the hidden information that would be difficult orimpossible to simulate.

Modules can be complete functional devices, such as batteries,actuators, joints, transistors, etc., which can be freeform fabricateddirectly into other designs to produce a composition of higherfunctionality. Design rules can be empirical relations between, forinstance, the volume of active material deposited in a certain type ofdevice, and the performance of the resulting device.

In order for the manufacturing planning and control system to be able toautomatically monitor the progress of a fabrication operation, toidentify and locate objects placed in the build environment, and tomeasure the geometry of the finished product, the system may include anon-contact ranging sensor device which can be scanned by thepositioning system across the build surface (i.e. substrate). Thisdevice has a distance resolution of 10 micrometers, while thepositioning system has an XY-plane resolution of 5 micrometers. Thebenefit of this type of sensor is that it is compact enough to embedwithin material deposition tools near the point of material deposition(e.g. nozzle), and of low enough cost to use in each cartridge, even inmultiples. The presence of the ranging sensor within a materialdeposition tool permits the acquisition of the geometry of depositedmaterial with minimal interruption of the fabrication process (e.g.without pausing manufacturing in order to mount a separate sensing toolto perform the scanning) and very near the point of deposition. Thisimproves the value of the resulting data for use in feedback control ofthe deposition tool—geometric flaws in deposited material can bedetected quickly, minimally allowing the manufacturing planning softwareto design compensating material deposits which can be executed in atimely fashion, without compromising the properties of materials whichare sensitive to the time since deposition. If such sensing can beprovided in a 360 degree circle around and very proximate to the pointof deposition, such sensing could be used for online feedback control ofthe deposition tool—allowing the control law for the tool to adjust toolactuator commands in order to achieve the desired deposit geometry.Because many materials are not mechanically durable, and many areliquids, measurement by contact methods is not acceptable for this role.Even if not useful for online feedback control, more frequent“semi-online” feedback provided by the currently employed sensor greatlyimproves the achievable final quality of the object being fabricated,because it allows the manufacturing planning software to compensate forvariability in the properties of the materials being employed, or otherdeposition errors by automatically generating modified manufacturingplans which compensate for the errors, for instance by depositingmaterial into undesired gaps, or by modifying subsequent depositionpaths so that they do not collide with excess material that wasaccidentally deposited.

Alternative embodiments for this type of non-contact geometric sensingmay include confocal chromatic displacement sensor, ultrasonic rangesensor, a laser triangulation sensor as illustrated in FIG. 12 , whichcan provide superior distance resolution, and reduced sensitivity to thereflectivity of the material. Laser triangulation sensor 150 ispreferably positioned on the back side of tool interface 20 and emitslasers 152 onto substrate 16. Other machine vision sensing technologiesare also available, including microscopic video capture at the point ofdeposition.

One of the challenges of employing multiple tools in a freeformfabrication system is that of “registration,” namely ensuring that thepoint of material deposition is accurately known by the systemcontroller for each tool that is used. The tools have finite rigidity,and even using precision robotic tool changers to mount tools to thepositioning system, there is a limit to the repeatability of theposition of the point of action of the tool. Without accurateregistration, material deposited by one tool will not be positionedcorrectly relative to material deposited by previous and subsequenttools used, and significant geometric and functional errors will resultfrom the manufacturing process.

Two approaches have been explored for calibrating the location of thepoint of deposition. The first, and inferior method, requires that foreach time a tool is mounted for use on the positioning system, a humanoperator must manually control all 3 axes of the positioning system,placing the tip of the tool in contact with a “registration mark” on thebuild surface. The position of this mark is stable over time and at aknown location within the volume accessible to the positioning system.Thus, when the point of deposition of the current tool is located atthis mark, the positioning system can read the displacement between thislocation and the known location of the registration mark, and therebyinfer the position of the point of deposition of the current tool.Because this method requires an operator to perform the calibrationmanually through visual alignment, and for each tool change, the laborand time required are impractical (1-5 minutes for each calibration,possibly hundreds of tool changes during a relatively simple buildoperation). For this reason, a second method has been developed whichautomates this calibration process. As illustrated in FIG. 13 ,calibration device 44 is mounted on substrate 16. Calibration device 44eliminates the need for the registration mark and reliance on the humanoperator's eye. Calibration device 44 has two infrared emitters 200A-Band two infrared detectors 202A-B oriented orthogonally to each other,and Teflon-covered analog force sensor 204 located at the intersectionof the two optical axes.

The optical emitter/detector pairs (200A-B and 202A-B, respectively)function by detectors 202A-B returning a signal level which is higherwhen less infrared light is received from emitters 200A-B. Thus, when anobject obstructs the optical axis of an emitter/detector pair, thesignal will be larger than when no object is present, and the signalvaries symmetrically as an object moves perpendicularly across theoptical axis. This sensing arrangement easily detects small depositiontips, such as a syringe needle 68 with an outside diameter of 0.007″.The system control software monitors the analog output signals from theoptical sensors, while commanding the positioning system to perform asearch pattern. When tool tip 68 has been positioned at the center ofboth optical axes, providing the X and Y coordinates of the tool tip,the Z-axis is elevated gradually, raising the sensor assembly towardtool tip 68 until a signal is detected by force sensor 204. Force sensor204 is designed to detect very small changes in applied force with verylittle displacement, so detecting contact with the sensor requires verylittle force be applied to tool tip 68. When a threshold force isdetected, the Z coordinate of tool tip 68 is identified.

In an alternative embodiment of calibration device 44, a hole is left inthe center of sensor 204, extending directly through substrate 16. Aninitial rough positioning of tool tip 68 will be used to maneuver tooltip 68 through the hole so that it extends below the plane of substrate16. A compressed gas jet located beneath the substrate 16 at thislocation will be activated briefly to blow away any residual materialattached to tool tip 68, if the tool is delicate. If tool tip 68 is lessdelicate and requires more vigorous cleaning, a wire brush, rubberscraper blade, or similar device will be located proximate tocalibration device 44 to be used for tip cleaning (by relative motion).Tool tip 68 will then be raised upward through the hole, and the searchpattern used to identify the X, Y, and Z coordinates of tool tip 68—theX and Y coordinates first as before with the current version of thesensor, and the Z coordinate by observing simultaneous rising signaledges in detectors 200A-B which is associated with tool tip 68 leavingboth optical axes simultaneously in the Z-direction.

Before commencing to fabricate an article and/or after having made eachdeposit of material, the system can collect 3-dimensional geometry dataof the current state of the substrate and any objects therein, thematerial deposited, and the article being fabricated. Preciselycapturing the geometry of the substrate immediately prior tomanufacturing, planning, and commencing deposition is important when anarticle is to be fabricated onto or into an object whose geometry andlocation are not precisely known, are not easily represented, and/or arenot static, such as a living organism. This permits the manufacturingplan to be generated in a manner which accommodates the actual geometryof the substrate, preventing collision between the deposition tool andthe substrate, and improving deposition quality by maintaining properseparation between tool and substrate. The more dynamic the substrate,the more frequently such data must be captured. If necessary, geometricsensing apparatus can be located very near to the orifice of a tool anddata collected continuously, enabling the system controller to track themotion of the substrate and command compensatory motion of thedeposition tool relative to the substrate while depositing material inorder to achieve the desired deposit geometry. After having made adeposit of material, the system can collect 3-dimensional geometry dataof the current state of the product being fabricated. Any substantialunexpected deviation of the deposit geometry from that predicted by themanufacturing simulation for the current manufacturing step will becaptured as an error volume (polytope). This error volume will be sentback to the manufacturing planning software which may modify themanufacturing plan in order to attempt to remove the error by makingadditional material deposits, or may cancel the entire manufacturingoperation. Any unremediated error will be incorporated into themanufacturing simulation, to improve prediction of the characteristicsof the finished product. This error data may also be used to modify thematerials/tools/substrates and design databases to reflect any knowledgegained from identifying the cause of the error. Other sensing devicesmay be used in an analogous manner to provide spatial and/or temporalmonitoring of other aspects of the substrate, of the state of thematerial being deposited, and of the article being fabricated.Deviations of the measurements from the desired values, as simulated inthe simulation module of the system software, or as expected from thedata in the materials/tools/substrates database, can be used to generatecompensatory actions which may be executed prior to making the nextdeposit of material. For instance, given a deposit of a chemicallyreactive material which changes color as it reacts, a machine visionsensor can detect that the color of a region of deposited material isnot what is expected for this material given the data present in thematerials/tools/substrates database, the time elapsed since the materialwas deposited, and the conditions experienced by the material asmeasured by sensors within the substrate module. The system can generatea compensatory action which is to apply local heating via a materialmodification tool to those areas which are under reacted, and to reducethe temperature in the receptacle of the substrate module in order toslow the reaction of those areas which are overreacted.

To further enable fabrication of complex articles, such as livingtissues, the fabrication system of the present invention may have one ormore substrate modules attachable to the substrate. FIGS. 14A-Cillustrate a module of the present invention, which is attachable to thesubstrate. Module 300 has housing 302 and lid 304, which rests onhousing 302. Module 300 is also provided with auxiliary materialinterfaces 310 and electrical interface 312. Material is dispensed froma material deposition tool into receptacle 306. Alignment sockets orpins are located on the base of module 300 and/or at the periphery ofelectrical interfaces 310 and/or auxiliary material interfaces 312 toassist in aligning of module 300 with other modules and/or withelectrical and auxiliary materials interfaces of the material depositiondevice and/or of the tool rack or other storage system. In addition, thealignment sockets and/or the electrical interfaces and/or the auxiliarymaterials interfaces of module 300 may be connected to mating interfaceson a transfer system in order to minimize the amount of time that module300 spends disconnected from utilities, materials, and communicationswith the rest of the article fabrication system. Fixture points 308 arepositioned on lid to assist in securing and positioning foreign objects,such as sensors, exogenous devices, or living organisms within thereceptacle so that material can be deposited onto or into them.

FIG. 15 is a perspective view of module 300, which illustratesreceptacle 306. Receptacle 306 is a special region of module 300 that isintended to receive material dispensed from a material deposition tool.Receptacle 306 is specialized to suit the properties and needs of thematerial and/or the component being fabricated. In one embodiment,receptacle 306 is a simple flat surface, a Petri dish, a foam structure,or a geometrically complementary or semi-complementary surface.Receptacle 306 may contain a liquid, gas, and/or solid, such as acrosslinking solution. To support in vivo fabrication, receptacle 306may be or contain part or all of the body of an organism. To supportthis type of receptacle, module 300 may have fixture points 308 to whichclamps or dissecting tools may be attached in order to hold the organismor object in a manner which assists the material dispensing process.Located inside of receptacle 306 are sensor ports 314 and auxiliarymaterial ports 316. Sensor ports 314 enable monitoring of the conditionsinside receptacle 306 before, during, and after the fabrication process(i.e. the dispensing of material into receptacle 306. Auxiliary materialports 316 are openings through which auxiliary materials enter or leavereceptacle 306.

In a preferred embodiment, receptacle 306 is provided with enclosure 318illustrated in FIG. 16 . Enclosure 318 provides a controlled (e.g.sterile) environment for receptacle 306. In one embodiment, enclosure318 is a permeable barrier or boundary and material is deposited from amaterial deposition tool into the enclosure by piercing the enclosure.In an alternative embodiment, enclosure 318 is a non-permeable barrieror boundary. In a preferred embodiment, enclosure 318 is provided withan access port through which material dispensed from a materialdeposition tool may penetrate enclosure 318.

FIG. 17 is an exploded perspective view of module 300. Housing 302 isprovided with channel 336, which houses electronics module 326 andelectrical wiring 324. Port 330 allows exposure of electrical interface312 for connection of electronics module 326 to an on-board controlleror the system controller. Electrical interface 312 operably connectsmodule 300 to the rest of the fabrication system and/or to othersubstrate modules. Electrical interface 312 also permits sending and/orreceiving of signals (wired or wireless) and/or power. A preferredelectrical interface 312 includes, without limitation, mateableelectrical connectors, umbilicals, and optical or radiofrequencytransceivers.

Electronics module 326 contains any signal conditioning and processingrequired to operate and monitor whatever sensors and actuators are inmodule 300. Electronics module 326 may also contain local intelligenceand control, local power, and communications devices associated withmonitoring/controlling, powering, and communication for module 300. Thesignals and power flowing between electronics module 326 and the sensorsand actuators within substrate module 326 (including those that might beattached to or embedded within an organism, object, or device attachedto module 300) flow through conduits such as wiring, cables, orwirelessly.

Sensing control in receptacle 306 is carried out as the environment inreceptacle 306 is sensed through sensor ports 314 and communicated viaelectrical wiring 324 to electronics module 326. Thus, in a preferredembodiment, substrate module 300 is equipped with sensors. Sensors ofmodule 300 monitor the state of module 300 and its contents. Forexample, the sensors of module 300 may be a sensor for light,temperature, fume presence, humidity, fluid presence, deposited materialpresence, auxiliary material flow rate, acceleration, mechanical force,electrical current, electromagnetic fields, materialconductivity/resistivity, color, spectral absorptivity/reflectivity,vital signs, and/or tilt angle. Sensors may be positioned anywherewithin module 300 or its contents, for instance, embedded in an organismcontained within/mounted to module 300, and may be monitored via wire orwirelessly by the local intelligence and control of module 300, ordirectly by the system controller.

Channel 338 houses auxiliary materials control module 322 and auxiliarymaterials tubing 320. Electrical control and sensing signals andelectrical utilities required by the auxiliary materials control module322 may be supplied via connection of auxiliary materials control module322 to electronics module 326 via wiring routed internally to module300, running directly from channel 338 to channel 336. These signals mayalso be routed via electronics interface 312 in order to permit them tobe connected thereby to the system controller, to the electronicsmodules 326 and auxiliary materials control modules 322 of othersubstrate modules 300, substrate 16 of the material deposition device,and/or to module storage and/or transfer devices.

Auxiliary control of receptacle 306 is carried out as auxiliarymaterials are distributed and/or collected throughout module 300,including to and/or from devices or organisms positioned in receptacle306, via auxiliary material ports 316 and auxiliary conduits 320 which,in a preferred embodiment, are pipes, channels, or tubing. Auxiliarymaterial control module 322 contains mechanisms, sensors, or actuatorsdirectly associated with sensing and control of the auxiliary materials.These may, in turn, be connected to electronics module 326, or may beinterfaced directly to the system controller (e.g. through electronicsinterface 312). Auxiliary material control module 322 may containvalves, flow sensors, mixing devices, regulators, and/or vibrators.

Auxiliary material interfaces 310 send or receive auxiliary materialincluding, without limitation, solids, fluids, and/or gases to and/orfrom receptacle 306 via auxiliary material ports 316. Auxiliary materialinterfaces 310 may mate with auxiliary material interfaces of otherparts of the fabrication system, including other substrate modules,substrate module storage (e.g. a tool rack), transport devices, orsubstrate 16 of the material deposition device. For example, auxiliarymaterial interfaces 310 could provide module 300 with cell culture mediaor other nutrients, pressurized fluids for power, gas supplies foratmospheric control, heated or cooled fluids for heat exchange, and/orclear module 300 (i.e. receptacle 306) of waste material.

In a preferred embodiment, module 300 is also equipped with actuators,which change and/or maintain the state of module 300 (i.e., receptacle306) and its contents. Actuators may be located anywhere within module300 or its contents, and may be controlled via wire or wirelessly by thelocal intelligence and control of module 300, or directly by the systemcontroller. For example, actuators may provide active supply orsuppression of light, UV light, vibration, ultrasound, heat, humidity,contaminants, mechanical forces, mixing, electromagnetic fields, or gasmixtures. Other examples of auxiliary control include fluid pumping orflow regulation, receptacle tilting, and/or auxiliary material pumpingor flow regulation. These operations may include controlling the stateof a living organism or a complex device attached to or contained withinthe receptacle—for instance providing intravenous materials, ormechanical or electrical stimuli. This can be useful in the fabricationand development of tissues which require external stimuli for properformation, such as bone, or in the continual operation of complexdevices, such as sensor arrays or micropumps, whose state can becontrolled even as material is being deposited on and around them.

The local intelligence and control of module 300, which may reside inelectronics module 326 of module 300, preferably controls theaforementioned actuators and sensors of module 300 alone or incooperation and communication with the system controller. It may performthis sensing and control based upon its own program, or in concert withthe manufacturing plan which resides in the software of the systemcontroller. The local intelligence and control of module 300 may alsolog data such as the commands given to actuators or feedback fromsensors.

The local power of module 300 provides power to module 300 in the casethat module 300 is not supplied with external power. Local power may beincluded within electronics module 326. In a preferred embodiment, thelocal power includes, without limitation, batteries, capacitors, fuelcells, and/or photovoltaic cells. Local power, for example, enablesmodule 300 to continuously log data, sense and control its own state,and the state of its contents, even when disconnected from the rest ofthe fabrication system.

Module 300 may also have heating/cooling element 332 to providetemperature control of receptacle 306.

Lid 304 and bottom lid 334 contain substrate module 300.

As shown in FIG. 18 , module 300 is attachable to substrate 16 of thematerial deposition device of the present invention. Mechanicalattachment of module 300 to substrate 16 may, for example, be carriedout through one or more of the following means: alignment pins orsockets, bolts, vacuum chuck mating surfaces, rails, and/or magnets,adhesives, or inter-surface friction. In a preferred embodiment, module300 attaches to module interface bar 340 positioned on substrate 16.Module interface bar 340 is preferably equipped with one or more dockingstations, each docking station having electronic interface 342connectable to electrical interface 312 and auxiliary material interface344 connectable to auxiliary materials interface 310. Together, thesemechanical, electrical, and auxiliary materials attachments allow theprecise and repeatable positioning, electrical communication andutilities supply, and auxiliary materials supply and return of one ormore units of module 300 during the time in which module 300 residesatop substrate 16 during the course of article fabrication. In FIG. 19 ,module 300, which is equipped with enclosure 318, is attached tosubstrate 16.

In a preferred embodiment, module 300 is disposable or containsdisposable components, for instance to improve sterility.

Module 300 may be manually or automatically transported to/from thematerial deposition device. In a preferred embodiment, module 300 istransported by the transfer device of the system of the presentinvention.

When employed in the fabrication system of the present invention, module300 serves the purpose of receiving the dispensed material in a fashionthat supports the objective of the fabrication. Module 300 provides alocal environment for the dispensing region and a surface that issuitable for fabrication. Module 300 may monitor and/or control, aloneor in concert with the system controller, a variety of sensors andactuators which interact with the contents of the substrate module. In apreferred embodiment, module 300 has a local intelligence and controland/or local power. Alternatively, module 300 is operably connected tothe system controller. Module 300 may be connected to and/or incommunication with the system controller before, during, and/or after afabrication process, for instance to allow monitoring and control ofmodule 300 and its contents to be an integral part of a manufacturingplan executed by the system controller.

Suitable deposition materials for use in the system of the presentinvention include, without limitation, any material capable of beingdeposited from a material deposition tool onto the substrate. The typeof material preferred will depend on the type of material depositiontool being employed. For example, when a fusible-material extrusion toolis employed, suitable materials include, without limitation, thermallyliquefied plastics, low melting-point metals, and other fusiblematerials. When a syringe cartridge is employed, suitable materialsinclude, without limitation, virtually any liquid, slurry, or gel.

Using a given material with a solid freeform fabrication systemtypically requires modifying that material somewhat to make it useableby one of the tools within the system, or at an extreme, development ofan entirely new tool. If it is desired that the new material should beable to be incorporated into designs made with a variety of materials,then a significant amount of effort is required to ensure compatibilityof materials and processes, to develop operating parameters for tools,and to fully characterize the resulting materials, deposits, andgenerate all of the data required to enable the system to make full useof the material. For this reason, each successful material formulationis a significant achievement in itself. Several such formulations havebeen developed, including tissue engineering materials, zinc-air batterymaterials, polymer actuator “artificial muscle” materials, and others.

Methods such as molecular self-assembly can be combined with this systempermitting localized self-assembly of molecular level structures.Ink-like materials can be made which are MEMS devices dispersed in aliquid carrier. The MEMS devices can be deposited as a normal ink. Afterevaporation of the carrier, the devices can be electrically connected bydepositing electrically conducting materials in appropriate patterns.

Novel applications of this system in the areas of biomedical implantscan include controlling the biocompatibility of conventionallymanufactured biomedical implants by depositing compatible livingtissues, or appropriate chemicals, as a covering for the devices. Novelbiomedical implants can be produced which are hybrids of freeformfabricated materials—both biological and non-biological—withconventionally manufactured devices which are embedded within. This canresult in implants which have functionality that is unachievable byconventional manufacturing means.

For most purposes, the system should be enclosed. The enclosureprimarily serves two purposes: safety and manufacturing environmentcontrol. The enclosure includes fume extraction filtration and/orducting connections to external ventilation in order to allow use of thesystem in a human occupied space. The enclosure also prevents humanoperators from contact with high temperatures, high voltages, laserradiation, etc.

The enclosure also permits the system to control the ambient environmentin which fabrication takes place. Temperature, humidity, and gas mix ofthe environment, as well as illumination can all be controlled overtime. This permits the system to control the evolution of the propertiesof deposited materials over time. For instance, the system can maintaina low temperature to limit chemical reaction until all of a certainmaterial has been deposited, then cause reaction in the depositedmaterial by elevating the temperature, or viability of living tissuesbeing deposited can be enhanced by maintaining incubating conditions.

For certain purposes, especially when working with very sensitivematerials, or under very stringent sterility conditions, it may bedesirable to include a “local enclosure” around the object beingfabricated. This can take the form of a sterile and/or sterilizablemembrane or bag which encloses the active region of the substrate, andwhich can be penetrated by the tip of a tool in a selective fashion.This arrangement permits the upper surface of the membrane to move withthe tool while the lower surface remains stationary relative to thebuild surface and the object being fabricated. Such local enclosurescan, for instance, permit use of a version of the fabrication system notspecifically designed for sterile work to work with materials whichrequire high standards of sterility, further enhancing the breadth ofutility of the system for exploring freeform fabrication with novelmaterials without extensive specialized modifications specifically forthose materials.

Systems of the present invention may be used in the fabrication of avariety of articles including, without limitation, the fabrication offood products. For example, a system of the present invention issuitable as a household product for production of breads, pastries,cakes, candies, or other food items. Such food items could beconstructed using systems of the present invention to produce foodarticles with various 3D shapes and internal structures (e.g., a patternthat reveals an inscription when a slice is taken, or in various 2D or3D shapes downloaded from the internet). When fabrication systems inaccordance with the present invention are employed in the production offood items, material deposition tools of the present invention mayinclude, without limitation, food processing devices and substrates mayinclude, without limitation, modules suitable for baking and/or cooking.

Another aspect of the present invention relates to a method offabricating an article. This method involves providing theabove-described article fabrication system. Material is dispensed fromthe material deposition tools, when mounted on the tool interface of thematerial deposition device, in amounts and at positions on the substratein response to instructions from the system controller, whereby anarticle is fabricated on the substrate.

In a preferred embodiment, the article fabricated by the method of thepresent invention is a living tissue.

A preferred material according to the method of the present invention isa material having seeded cells, preferably a hydrogel having seededcells. Suitable hydrogels include, without limitation, alginate,agarose, collagen, chitosan, fibrin, hyaluronic acid, carrageenan,polyethylene oxide, polypropylene oxide, polyethyleneoxide-co-polypropylene oxide, hydroxypropyl methyl cellulose,poly(propylene fumarate-co-ethylene glycol), poly(ethyleneglycol)-co-poly(lactic acid), poly(vinyl alcohol), KDL12 oligopeptides,and poly(n-isopropyl acrylamide).

The hydrogels preferably have a controlled rate of crosslinking throughthe adjustment of environmental variables including, but not limited to,temperature, pH, ionic strength, heat, light, or the addition ofchemical crosslinking agents such as calcium, magnesium, barium,chondroitin, sulfate, and thrombin. The cross-linking compound ispreferably provided in a weight ratio of hydrogel to cross-linkingcompound of about 1:100 to 100:1, respectively. In a more preferredembodiment, the weight ratio of cross-linking compound to hydrogel isabout 1:5.3. In an even more preferred embodiment, the cross-linkingcompound is calcium sulfate.

In one embodiment, cells in the hydrogel are of a single cell type.Suitable cell types include, without limitation, all mammalian or plantcells. Preferred cell types include, without limitation, chondrocytes,osteoblasts, osteoclasts, osteocytes, fibroblasts, hepatocytes, skeletalmyoblasts, cardiac myocytes, epithelial cells, endothelial cells,keratinocytes, neurons, Schwann cells, oligodendrocytes, astrocytes,pneumocytes, adipocytes, smooth muscle cells, T cells, B cells,marrow-derived stem cells, hematopeotic stem cells, osteoprogenitorcells, neural stem cells, and embryonic stem cells. Alternatively, cellsin the hydrogel may be of more than one cell type.

Dispensing material from the material deposition tools, according to themethod of the present invention, is preferably carried out under sterileconditions. In one embodiment, dispensing of the material may be carriedout in a hermetically sealed envelope.

The method of fabricating a living tissue may further involvedetermining geometry and cell distribution of the article prior tocarrying out the dispensing step. The system controller may also beprogrammed with instructions effective to cause the dispensing steps tobe carried out to produce an article with a desired geometry and celldistribution.

In one embodiment, the determined geometry is free-form. In analternative embodiment, the geometry is an anatomic shape, preferablypatient-specific.

To determine geometry, a computerized scan of a tissue/organ may begenerated, such as a scan of a tissue/organ to be replaced. The geometryto be dispensed can be determined from any method capable of generating2D and/or 3D data sets, including, without limitation, 3D laserscanning, confocal microscopy, multi-photon microscopy, computerizedtomography, magnetic resonance imaging, ultrasound, and angiography.

After a hydrogel with seeded cells is fabricated pursuant to the methodsof the invention, the article may be incubated under conditionseffective to grow the cells. Incubation may be carried out on thesubstrate, or the article may be transferred to a new substrate for moreoptimal growth conditions.

A further aspect of the present invention relates to a method offabricating a living three-dimensional structure. This method involvesproviding a data set representing a living three-dimensional structureto be fabricated. One or more compositions including a compositionhaving a hydrogel with seeded cells is provided. The one or morecompositions are dispensed in a pattern in accordance with the data setsuitable to fabricate the living three-dimensional structure.

Suitable compositions for carrying out this method include hydrogels,with or without seeded cells, which in a preferred embodiment, containcross-linking compounds to provide structure to the fabricated tissue.

EXAMPLES

The examples below are intended to exemplify the practice of the presentinvention but are by no means intended to limit the scope thereof.

Example 1—Direct Freeform Fabrication of Living Pre-Cell-Seeded AlginateHydrogel Implants in Anatomic Shapes

Articular chondrocytes were isolated from cartilage from thefemeropatellar groove of 1-2 week old calves by collagenase digestion(Genes et al., “Effect of Substrate Mechanics on Chondrocyte Adhesion toModified Alginate Surfaces,” Arch. Biochem. Biophys. 422:161-167 (2004),which is hereby incorporated by reference in its entirety). Chondrocyteswere suspended in 2% ultrapure low viscosity alginate in phenobarbitalsodium (“PBS”) at a concentration of 50 million cells/mL. The suspensionwas vortexed and mixed with 10 mg/mL CaSO₄ in PBS in a 2:1 ratio. Thegel was placed in a sterile 10 mL syringe with a 22 gauge SafetyLoktapered syringe tip and loaded into a gel deposition tool.

In parallel, a computerized tomography (“CT”) scan of an ovine meniscuswas converted into a stereolithography file using Microview software.The file was then imported into a custom software package and was usedto plan tool paths for the gantry robot. The gantry robot moved the geldeposition tool in prescribed tool paths and fabricated the implant in alayer-wise fashion. After printing, the implant was soaked in a 20 mg/mLCaCl₂ solution in PBS for 30 minutes to further cross-link the gel.Finally, the gel was transferred to Dulbecco's minimal essential medium(“DMEM”) growth media with 10% fetal bovine serum.

The viability test was performed with a live/dead viability assay using0.15 μM calcein AM and 2 μM ethidium homodimer-1 (EthD-1) and a stainingtime of 35 minutes at room temperature. Samples were analyzed in aBright Line counting chamber using a Nikon TE2000-S microscope equippedwith an epifluorescence attachment and a Spot RT digital camera.

The sterility test was performed by culturing a printed sample in growthmedia without antibiotics for 8 days. Bacterial presence was tested forin the cultured sample with 100 μM BacLight Green bacterial stain aBright Line counting chamber, and a Nikon TE2000-S microscope equippedwith an epifluorescence attachment and a digital camera.

The technique used to mix the alginate and crosslinker has a strongeffect on the physical properties of the gel (Hung et al., “AnatomicallyShaped Osteochondral Constructs for Articular Cartilage Repair,” J.Biomech. 36:1853-1864 (2003), which is hereby incorporated by referencein its entirety). The mixing technique that yielded a “printable” gelinvolved 10 full-cycle pumps between two 10 mL syringes through astopcock over a total of 10 seconds.

Viability tests successfully detected both live (FIG. 20A) and dead(FIG. 20B) cells in printed gels. Based on this data the viability ofthe printing process was determined to be 94±5% (n=15). After 8 days ofincubating a printed gel sample without any antibiotics in growth media,less than 1 bacterium per 0.9 μL was detected (n=12).

Using a CT scan of bovine meniscus, an STL file was generated (FIG. 21A)and used to plan the robot's tool paths. The printed meniscus-shaped gel(FIG. 21B) had a geometric resolution of 0.4 mm. The total printingtime, from when the deposition tool was loaded with gel to the end ofthe print-job, was less than 6 minutes.

This research demonstrated the use of an open-architecture roboticprinting platform to successfully 3-D print infection-free, living,preseeded hydrogel implants of anatomic geometries. One of the greatestchallenges was changing the formulation of a moldable hydrogel into onethat is “printable.” Formulation concentrations were adjusted to set acrosslinking rate that was fast enough for the deposited gel to hold itsshape yet slow enough to prevent material shearing upon deposition.Other tissue engineering technologies such as injection molding (Changet al., “Injection Molding of Chondrocyte/Alginate Constructs in theShape of Facial Implants,” J. Biomed. Mat. Res. 55:503-511 (2001), whichis hereby incorporated by reference in its entirety) or casting (Hung etal., “Anatomically Shaped Osteochondral Constructs for ArticularCartilage Repair,” J. Biomech. 36:1853-1864 (2003), which is herebyincorporated by reference in its entirety) have the potential to produceanatomically shaped implants. However, these require the use of negativetemplates which may be difficult or impossible to produce in extremelycomplex geometries. Further, the elimination of the mold decreases thetime necessary for implant production. An additional advantage of thistechnology is that the system has been designed to handlemultiple-material print jobs (Malone et al., “Freeform Fabrication of 3DZinc-Air Batteries and Functional Electro-Mechanical Assemblies,” RapidPrototyping Journal 10:58-69 (2004), which is hereby incorporated byreference in its entirety). This capability to print gel implants ofmultiple types of gel enables the fabrication of implants with spatialheterogeneities distributed in prescribed positions with a geometricresolution of 0.4 mm. The ability to rapidly fabricate implants withspatial heterogeneities in cell-type or concentration would be a greatadvantage in producing tissues such as articular cartilage, meniscus, orintervertebral discs that contain multiple cell types of distinctdistributions.

Example 2—Direct Freeform Fabrication of Spatially Heterogeneous LivingCell-Impregnated Implants

Robotic Test Platform

An open-architecture gantry robot has been designed and used in thisresearch (Malone et al., “Freeform Fabrication of 3D Zinc-air Batteriesand Functional Electro-mechanical Assemblies,” Rapid Prototyping Journal10:58-69 (2004), which is hereby incorporated by reference in itsentirety). The tool paths are generated by path planning software, whichtakes multiple stereo lithography files corresponding to multiplematerial types as input. This system has been designed to allow theprinting of multiple materials within a single part. This capability isused to print multiple gels with varying cell types, chemicalconcentrations, cell densities, etc. The robot is capable of moving thedeposition tool to a specified position with accuracy and repeatabilityof ±25 μm. The full specifications of this robotic system are given inTable 1.

TABLE 1 Fabrication System Performance Specifications Minimum material250 μm 0.010M. stream/drop diameter Materials cross-section area 4.9 ×10⁻⁸m²  Build rate 2.5 × 10⁻⁹ m³/s 0.55 in.⁻³/h Nominal speed along path0.05 m/s Min.-turn radius at nominal 125 μm 4.92 × 10⁻³ in speed Toolposition accuracy (±) 25 μm 9.84 × 10⁻⁴ in Tool position repeatability25 μm 9.84 × 10⁻⁴ in (±) Positioning resolution 5 μm 1.97 × 10⁻⁴ in.Build envelope x 0.3 m 11.8 in. Build envelope y 0.3 m 11.8 in. Buildenvelope z 0.3 m 11.8 in. Max. XY acceleration 20.75 m/s² 2.12 g 

Gel Deposition Tool

The gel deposition tool must accurately deposit gels while maintainingsterility. Additionally, the tool has to enable efficient materialchanging. Efficient swapping of sterile materials is important forprinting implants of multiple gels (each with different cell types,concentrations, etc.).

Through experimentation, it was found that elastic materials aredifficult to deposit with pneumatic dispensing systems and instead avolumetrically controlled dispensing system was chosen. An ABS plasticrapid prototyped frame connects a linear actuator to the syringecartridge. Medical-quality sterile syringes are used as the disposablematerial cartridges of the deposition tool. Luer lock syringes wereselected in order to enable a wide variety of syringe tips to beutilized. Tool performance specification can be found in Table 2.

TABLE 2 Deposition Tool Performance Specifications Maximum appliedpressure 1592 kPa Cartridge volume 10 mL Maximum volumetric flow rate10.5 mL/s Deposition accuracy 0.000426 mL Deposition precision 0.000426mL

Sterile Printing Envelope

Sterile printing conditions are a paramount concern, the lack of whichwould allow the printed implants to become infected. Although, asdescribed above, a solution was found for keeping the material sterileduring deposition, a way of keeping the immediate environment sterilestill needed to be found.

One possible solution to this challenge was to build a sterile,hermetically sealed envelope around the immediate printing zone. While afull envelope that encompassed the printer was considered, an evensmaller envelope that surrounds only the printed piece was moredesirable.

A one mm thick, autoclavable, clear plastic bag was chosen as theenvelope. This bag could be loaded with a Pyrex Petri dish, sealed, andthen autoclaved to ensure that the entire inside of the bag, includingthe Petri dish, was sterile. At this point, the inside of the bag servedas a closed, sterile environment (FIG. 22 ). At the time of printing,the tip of the syringe and a section of the outside surface of the bagwere swabbed with 70% ethanol solution and then the syringe tip wasinserted through the bag. All deposited material was printed onto thesterilized Petri dish and surrounded by the previously autoclavedenvironment. After printing, the bag was taken to a sterile work hoodwhere the outside of the bag was sprayed with alcohol and the sample wasremoved (FIG. 23 ). The disposable autoclave bag could then be discardedand a new bag used for the next print.

Printable Gel Formulation

The gel was composed of two components: a solution of alginate and acalcium cross-linker solution. Even though there were only twocomponents, there were many experimental variables and it was achallenge to find a gel that was both supportive of cellular life and“printable.”

Formulation Constraints

The alginate gel had to be both suitable from biological and SFFstandpoints. In order for a gel to be considered biologically suitable,the alginate gel had to sustain cellular life.

In order to satisfy the SFF needs, the gel had to be “printable.” By“printable,” it is meant that the gel would (i) bond between layers,(ii) hold its shape against gravity, and (iii) cross-link slowly enoughto prevent cell and material shearing during printing.

Formulation Process

The first step was the identification of experimental parameters. Theseparameters were identified as: (i) the type of cross-linker, (ii) thecross-linker concentration, (iii) the molecular weight of the alginate(iv) the mannuronic acid to guluronic acid ratio of the alginate, (v)the concentration of the alginate, (vi), how long to mix the alginateand cross-linker together and with what force (vii), how long to let thegel cross-link before printing, (viii) the choice of additives, and (ix)the range of syringe tip diameters that can be used to print the gel.

Since two separate sets of needs—biological and SFF—had to be satisfiedby some single combination of the above nine parameters, eachparameter's effect on the biological and SFF qualities of the materialshad to be analyzed.

Biological Formulation Needs

From prior publications (Xu et al., “Injectable Tissue-engineeredCartilage with Different Chondrocyte Sources,” Plast. Reconstr. Surg.113:5 (2004), which is hereby incorporated by reference in itsentirety), it was thought that the gel would be viable, i.e., supportcellular life, as long as the alginate concentration was 2% inphosphate-buffered saline (“PBS”) and the cross-linker concentration wasless than or equal to 2% in PBS. A standard seeding density of 50million cells per milliliter of gel was also used. These establishedstandards served to constrain two parameters, hence they simplified theformulation process by eliminating two variables.

SFF Formulation Needs

While the biological needs were satisfied by the aforementionedpublished standards, the SFF-related needs had yet to be satisfied.Extensive experimentation ensued in order to determine what effects thenine experimental parameters had on the three SFF-related materialproperties: (i) bonding between layers, (ii) resistance to weightinduced deformation, and (iii) prevention of shearing due to rapidcross-linking.

Inter-Layer Bonding Experiments

To study the effects of the nine parameters on the first SFF-relatedneed (namely, bonding between layers), it was determined that thisbehavior was directly related to the rate and amount of cross-linking atthe time of printing. Gels that cross-linked more quickly would befurther cross-linked at the time of deposition and would be lessreceptive to subsequent layers because the bonds were already formedbefore the following layers could be deposited. Experiments were run inwhich the experimental parameters were varied and the cross-linking ratewas given a relative, qualitative measure depending on how quickly thegel stiffened. The relationships between the experimental parameters andthe ability of the gel to bond between layers are summarized in Table 3.The goal of this experiment was to find some combination of the nineparameters that yielded a gel which cross-linked as quickly as possible,yet still bonded between layers.

TABLE 3 Relationship Between Parameters and Successful InterlayerBonding Relationship with Successful Experimental Parameter BondingBetween Layers Increased alginate molecular weight (−) Increasedcross-linker concentration (−) Longer mixing time (−) Longer sittingtime before printing (−) Larger tip diameter (+)

Resistance to Weight Induced Deformation Experiments

In order to see what effect each parameter had on the second SFF-relatedneed (namely, resistance to weight deformation), each parameter's effecton the gel viscosity was studied using an automatic viscometer. It wasinitially thought that the viscosity would be an accurate indication ofhow well the gel would hold its shape against gravity. In order tofurther vary the viscosity, dextrose was used as a bulking agent.However, after comparing the results of the viscosity experiments tosimulated prints in which the gel was layered by hand, it was clear thatviscosity was not an accurate indicator of a gel's resistance toweight-induced deformation. The notion was rejected and this part of theformulation process was iterated. At this point, it was noticed that theresistance was strongly related to cross-linking rate. While a highviscosity did not help the gel hold its shape, partial cross-linkingdid. Therefore, the faster a gel cross-linked the better it would beable to hold its own weight. At this point, it was realized that twoSFF-related needs were directly determined by cross-linking rate, thatis, the bonding between layers and the resistance to gravity. However,these two needs were opposed to each other. A higher cross-linking ratewould help the gel hold its shape against gravity, while at the sametime it would make the layers less likely to bond with each other. Someacceptable compromise needed to be reached. The relationship betweenparameters and resistance to weight-induced deformation is summarized inTable 4.

TABLE 4 Relationship Between Parameters and Resistance to Weight-InducedDeformation Relationship with Resistance to Experimental ParameterWeight-Induced Deformation Increased alginate molecular weight (+)Increased cross-linker concentration (+) Longer mixing time (+) Longersitting time before printing (+) Larger tip diameter (+)

Cross-Linking Rate Experiments

The third SFF-related need (namely, prevention of material shearing dueto rapid cross-linking) was also directly related to cross-linking rate.If the material cross-linked too quickly, then the gel wouldsignificantly bond before being deposited and the bonds would be shearedupon passing through the constricted syringe tip. A summary of therelationship between cross-linking rates and the SFF-related needs canbe found in Table 5.

TABLE 5 Effect of Cross-linking Rate on SFF Needs SFF-Related Need HighCross-linking Rate Low Cross-linking Rate Bonding Between Layers willnot bond Layers will bond with Layers with each other (−) each other (+)Resistance to Gel can hold shape (+) Gel cannot hold Gravity shape (−)Prevention of Gel will shear and lose Gel will not shear (+) Shearingmechanical properties (−)

Manual Test Prints

In order to find a cross-linker type/concentration that was suitable forthe three SFF formulation constraints, various chemical combinationswere tested manually. An efficient and simple test that indicates aparticular formulation's printability is a conical stacking experiment.One half inch to one inch cones are deposited manually over a time rangefrom t=0 to t=20 minutes. Each stack's ability to hold its shape againstgravity is observed. Since the material properties are time dependent,testing over a large time period is important. Not only are qualitativetraits noted for each formulation, but also an optimal time frame foreach formulation is identified. In this optimal time frame, theproperties are suitable for printing. With some formulations, theoptimal time frame begins at t=0, but with others the optimal timewindow begins after a delay. The goal was to find a printableformulation with longest optimal time window.

Selected Formulation

The formulation used in the experiments reported herein is 2% protanalalginate (a high M-group alginate) in PBS and 0.5% calcium sulfate inPBS. The two solutions were mixed with each other in a 2:1 alginate toCaSO₄ ratio. Since the mixing technique greatly affects the resultinggel due to shear effects, it is important to mix the gel consistently.The mixing technique that was used was to take one 10 mL Luer locksyringe with alginate, another with cross-linker and mix the twoback-and-forth through a Luer lock stopcock. A successful mixingprocedure was 10 full-cycle pumps at a rate of 1 pump per second. Inconsideration of resolution and shearing constraints, a 0.030″ diametersyringe tip was chosen.

Unseeded Gel Printing Test

This experiment verified the ability of this system to print gels ofcomplex arbitrary geometries. In this experiment, various geometrieswere printed on the gantry robot in full-scale, non-sterile printingruns. The “proof of concept test pieces” illustrated in (FIGS. 24A-L)were chosen because they each demonstrate the unique capabilities ofthis technology and because they have interesting medical applications.

Viability of Seeded/Printed Gel Test

The viability test verified short-term cellular survivability. In otherwords, the test determined whether the gel sustained life throughout theprinting process, i.e., while being subjected to the shear forcesinduced by the deposition process. During viability testing, theprinting process was simulated and then the percentage of living cellsversus dead cells was measured before and after the simulated printingprocess. In order to count the percentage of living cells, twofluorescent chemical markers were used. Calcein acetoxymethyl (calceinAM) attaches to living cells and ethidium homodimer-1 (EthD-1) attachesto dead cells. Through the use of a fluorescent light source, amicroscope, and the appropriate optical filters, the living and deadcells were identified (FIGS. 25A-B). The viability test did not have tobe done under sterile conditions; the test was measuring short-termviability and infection would only have a long-term effect.

Process Sterility Test

The approach of using an autoclavable plastic bag as a printing envelopehad to be tested to verify that no bacteria or fungi were allowed toinfect the printed alginate gel. A sterile sample of alginate gel wasprepared and placed in a sterile syringe. This syringe was thentransported, with a sterilized syringe end-cap, to the printer and thefull printing procedure was executed. After the printing, the sample wasbrought back to a sterile work hood where the envelope was opened andthe sample removed. The gel sample was incubated for a period of eightdays. After this incubation period, the sample was analyzed for presenceof bacteria and fungi growth with the use of a chemical marker andfluorescence microscopy. It was determined that there was less than 1bacterium per 0.9 μL after 8 days of incubation.

Direct CT Scan Printing Test

This research additionally demonstrated the ability to efficiently printa hydrogel implant directly from a CT scan. A CT scan of a meniscuscartilage was provided by the Cornell affiliated Hospital for SpecialSurgery (HSS) and then converted into an STL file. The STL file was thenloaded into the CCSL software package and prepared for printing. Theresults of this direct CT Scan print are shown (FIGS. 26A-B and FIGS.27A-B).

These results show the ability to successfully 3-D print viable,infection-free, living hydrogel implants of multiple materials withcomplex biological geometries. By printing with alginate hydrogelspre-seeded with gels, this technology serves as a versatile tissueengineering platform on which spatially heterogeneous implants of variedseeding densities, chemical concentrations, cell-types, etc., can befabricated in arbitrary geometries. Additionally, the fabrication ofimplants generated directly from CT Scans brings this technology onestep closer to its clinical form. This will allow patients to have,within hours, a complex, living, pre-seeded, multi-cell-type implant,such as an intervertebral disk, produced from prior CT Scans of theirown healthy body parts.

Example 3—Direct Freeform Fabrication of Zinc-Air Batteries withTailored Geometry and Performance

In the following discussion, a cell is defined as a device that convertsthe chemical potential energy between its anode and cathode materialsinto electrical energy by means of redox reactions: reduction (electrongain) at the cathode, oxidation (electron loss) at the anode. A batterycomprises of one or more connected cells. The essential functionalcomponents of a zinc-air (“Zn-air”) cell are the anode terminal, cathodeterminal, anode, separator, catalyst, electrolyte, and casing. The anodeand cathode terminals are passive conductors that collect chargecarriers and allow connection to external loads. The anode (zinc in thiscase) is one of the two key reactants in the cell. The other keyreactant, oxygen, is derived directly from the atmosphere. The separatorprovides electrical insulation between the anode and cathode to preventinternal shorting, but must be permeable to electrolyte to allow ioniccurrent flow. The catalyst accelerates the rate of chemical reaction atthe electrolyte/atmosphere interface in a cell, improving power output.The electrolyte (aqueous potassium hydroxide (“aq. KOH”) in this case),provides a medium for ionic transport within the cell and a source ofions. The casing provides an enclosure for the battery materials,permitting the battery to be handled without exposing the handler to thechemical reactants therein, and restricting the exposure of thereactants to the atmosphere, so that the evaporative loss of water fromthe electrolyte is reduced while still permitting the diffusion ofatmospheric oxygen into the battery. The basic chemical reactions are:

At Air Cathode: ½ O₂ + H₂O + 2e →2OH⁻ At Zn Anode: Zn → Zn²⁺ + 2e Zn²⁺ +2OH⁻ Zn(OH)₂ Zn(OH)₂ → ZnO + H₂O Overall: Zn + ½O₂ → ZnO:E₀ = 1.65 VThus, the ideal output voltage of a zinc-air electrochemical cell is1.65V. In practice, modes of energy dissipation within the cell limitopen-circuit voltage to about 1.4V, and 1.2V under reasonable loadingconditions.

In order to produce a Zn-air battery in accordance with the freeformfabrication system of the present invention, for each of the materialsrequired to produce a battery, a formulation must be prepared which canbe readily, automatically dispensed by at least one of the materialdeposition tools. This formulation process presents a significantchallenge given the variety of materials involved. The availabilitywithin the system of multiple material deposition tools which make useof differing deposition processes provides greater freedom in the choiceof materials and reduces the number of restrictions associated withselecting and formulating materials. The fact that the form of thefinished battery is determined by the geometry data provided to thefabrication system permits a variety of single and multiple cellbatteries, and a variety of battery shapes to be constructed withoutreformulation of materials or modification of method of fabrication.

A set of experiments concluded with the successful fabrication of acomplete, functional Zn-air battery with the freeform fabricationsystem. The experiments (Malone et al., “Freeform Fabrication of 3DZinc-air Batteries and Functional Electro-mechanical Assemblies,” RapidPrototyping Journal 10:58-69 (2004), which is hereby incorporated byreference in its entirety) employed two separate material depositiontools—a fusible-material deposition tool and a prototype version of acartridge holding tool—with the freeform fabrication system to produce acomplete, functional zinc-air battery.

The fusible-material deposition tool was used to depositacrylonitrile-butadiene-styrene (“ABS”) thermoplastic as the casing ofthe batteries. As this material has been used with this tool in a widevariety of other experiments, no special formulation was required.

The cartridge holding tool was used to deposit four different materialsfrom four 10 mL disposable syringes, each syringe loaded with one offour materials. The first material was a methylcellulose gel filled withsilver powder in order to render it electrically conductive. Thismaterial was used to form the anode terminal and cathode terminal. Thesecond material was a slurry of zinc powder and aqueous potassiumhydroxide at 8 Molar concentration, with a nonionic surfactant added todisperse the zinc powder and reduce friction in the material. Thismaterial was used to form the zinc anode. The third material was aslurry of ceramic particles in water with an adhesive binder. Thismaterial was used to form the electrically insulating separator. Thefourth material was a slurry of manganese dioxide, carbon black, andaqueous potassium hydroxide. This material was used as the cathodecatalyst.

Each of these materials required careful adjustment of the relativeconcentration of ingredients and, sometimes, the inclusion of additionalingredients in order to arrive at a formulation that can be dispensedfrom a syringe without clogging the syringe. All of the formulations hadto be carefully tested and adjusted so that when deposited in thecorrect juxtapositions to each other, the aggregate behaved as a workingelectrochemical cell with reasonable power output. This is necessarysince some of the formulation modifications which enhance the ability ofthe material to be dispensed may interfere with the desiredelectrochemical reactions.

Once acceptable formulations were arrived at for each of the fourmaterials, a syringe needle was selected for that material which has acircular cross-section and an interior diameter as small as possiblewithout being prone to becoming clogged by the material. The selectionwas made by mounting a syringe needle on a given syringe filled with oneof the materials. The material was pushed through the needle manuallyusing a standard disposable syringe plunger. If the entire contents ofthe syringe (approximately 10 mL) could be pushed through the needlewithout a clog forming, the needle was considered acceptable, and thetest was repeated with a needle of smaller internal diameter. If a clogformed, a needle of larger internal diameter was tried. This process wasiterated until the smallest needle was found that does not experienceclogging.

Each material thus had an associated syringe needle which partiallydetermined the geometry of the deposits of material that can be extrudedfrom the syringe, and hence by the cartridge holding tool.

Other factors that affect the geometry of the deposits include theviscosity of the material, which determines whether it retains its shapeor flows after having been deposited. It is generally desirable infreeform fabrication that materials have high viscosity so that theyretain their shape upon being deposited, and can be stacked verticallywithout being contained or supported. Another factor is the height ofthe tip of the syringe needle above the surface onto which material willbe deposited. This height should be roughly equivalent to the internaldiameter of the syringe needle in order to achieve a roughly circularcross-section of deposited material. Yet another factor that affects thegeometry of the deposits is the acceleration and speed with which thematerial is extruded from the syringe by the cartridge holding toolrelative to the acceleration and speed with which the materialdeposition device moves the cartridge holding tool along a given pathover the substrate. When these speeds are matched, the material will bedeposited with roughly the cross-sectional dimensions of the syringeneedle.

A calibration procedure was used to identify the accelerations, speeds,and distances which generate uniform, repeatable, and well-controlleddeposits of material, as well as the relative position of the materialdeposition orifice of the tool to the position of the materialdeposition tool interface of the material deposition device. Thecalibration procedure was commenced for each material by entering thematerial name, the name of the material deposition tool used fordepositing the material, and the initial estimated accelerations,speeds, and distances for the material into thematerials/tools/substrates database of the system, mounting thecartridge holding tool onto the deposition device, loading a syringe ofthe particular material into a material cartridge and the cartridge intothe cartridge holding tool, and commanding the system to produce a testpattern of the particular material by depositing it onto a substrate.The quality and geometry of the deposited test pattern was evaluatedvisually and with a caliper by the operator to determine whether thematerial deposits began, ended, maintained continuity, and maintaineduniform cross-section as specified by the test pattern data. Theparameters in the materials/tools/substrates database were adjusted andnew test pattern deposits generated until the results were deemedsatisfactory. The cross-sectional dimensions of the satisfactorymaterial deposits were measured using the caliper. The height and widthof the cross section of the deposits were entered into thematerials/tools/substrates database with the other parameters. Theparameters which generated the satisfactory results were used by thesystem for all subsequent deposition, including during the fabricationof a complete working battery.

Once the cross-section dimensions of material deposits and associatedparameters were found for all of the materials, the battery to befabricated was designed using SolidWorks three-dimensional mechanicalcomputer-aided design (“MCAD”) software. The battery designed was of acylindrical shape. The design included an assembly of parts. A hollowcylindrical casing part contained stacked disk-shaped partsrepresenting, from bottom to top, anode terminal, zinc anode, separator,cathode catalyst, and cathode terminal. The top-most part was adisk-shaped lid with holes intended to allow atmospheric oxygen todiffuse into the battery. Care was taken to ensure that the dimensionsof each part of the battery assembly was larger than the cross-sectiondimensions of the material from which that part was to be fabricated.The data describing the geometry of the assembly (and all of the partstherein) was exported from the MCAD software as a set of STL formatgeometry data file.

The graphical user interface (“GUI”) of the system software of thefreeform fabrication system was used to import the STL filesrepresenting the geometry of the battery parts into the fabricationsystem. As the geometry of each part was imported, a shaded surfacerepresentation of the part was displayed to the user. The user used afeature of the GUI to assign a material from thematerials/tools/substrates database to the part. The casing and casinglid were assigned the fusible-material deposition tool and the ABSthermoplastic material. All other parts were assigned the cartridgeholding tool. The anode terminal and cathode terminal were assigned themethylcellulose material containing silver powder. The zinc anode partwas assigned the zinc anode paste material. The separator part wasassigned the separator ceramic slurry material. The cathode catalystpart was assigned the cathode catalyst slurry material.

Once all of the parts of the battery were imported into the system, theuser commanded the software to generate a manufacturing plan. Using thenames of the materials assigned to each of the parts, the manufacturingplanning module of the software queried the materials/tools/substratesdatabase for the cross-sectional dimensions of the materials. For eachpart, the planning module then uses the height of the cross-section ofthe material associated with that part to generate a family of parallelplanes normal to the vertical (Z direction) axis of the system, spacedby the cross-section height of that material. The intersection of thepart geometry with the family of planes is a family of closed curves(called “boundaries”) which are uniformly spaced in height. At theheight of each plane which intersected the part, the planning softwaregenerated a set of planar lines and curves (called “toolpaths”) in thearea enclosed by the boundaries, which resided in the horizontal (XY)plane at that height, and which are horizontally spaced from each otherby the width of the cross-section of the material. The manufacturingplanning software labeled the toolpaths with the name of the materialdeposition tool and the material associated with the part beingprocessed.

This process was repeated for each part in the assembly whichrepresented the battery to be fabricated, after which the manufacturingplanning module sorted the toolpaths into a list according to severalcriteria, including the height of the toolpaths exported the set oflabeled toolpaths (called the “manufacturing plan”) to the operationcontrol module of the system software.

The GUI informed the user that the manufacturing plan was completed. Theuser then commanded the system software to begin executing themanufacturing plan.

The operation control module performed a self-test routine for thematerial deposition device hardware. The operation control module thenexamined the first labeled toolpath in the manufacturing plan toidentify the material deposition tool and material required. In thiscase, the first tool required was the fusible-material deposition tool,and the material was ABS thermoplastic. The operation control moduledetermined that this tool was not yet mounted on the tool interface ofthe material deposition device. The GUI requested that the user attachthis tool to the tool interface. The operation control module thenqueried the materials/tools/substrates database for the parametersassociated with this tool and this material, which also included thelocation of the material deposition orifice of the tool relative to thelocation of the tool interface in the material deposition devicecoordinate system. The GUI then requested that the user command motionof the positioning system of the material deposition device until theorifice of the material deposition tool was adjacent to the desiredpoint on the substrate at which the fabrication of the battery wasdesired to commence. The user employed the GUI to perform this action,and to inform the operation control module that this action wascompleted. The operation control module then recorded this position ofthe positioning system as the “build origin,” and commenced to commandthe positioning system to trace out the first path in the manufacturingplan while simultaneously commanding the material deposition tool todeposit material onto the substrate, coordinating the commencement andtermination of material deposition with the commencement and terminationof positioning system motion along the path. Once this path wascompleted, subsequent paths in the manufacturing plan were examined bythe operation control module. Several paths which described the bottomof the battery casing were executed in succession, resulting in a diskof ABS thermoplastic.

The next several paths in the manufacturing plan were labeled with thecartridge holding tool and the silver-filled methylcellulose material.The fabrication process was interrupted by the operation control module,which commanded the positioning system to move to a corner of its rangeof motion while employing the GUI to request that the user remove thefusible material deposition tool from the tool interface, and replace itwith the cartridge holding tool and ensure that a cartridge containing asyringe filled with the silver-filled methylcellulose material wasmounted in the cartridge socket of the tool. The user performed theseactions and signaled their completion using the GUI. The operationcontrol module then resumed the fabrication process by querying thematerials/tools/substrates database for the orifice coordinates for thistool and material, and adjusting the positioning system coordinatesystem to reflect the difference in the orifice coordinates between thetwo tools. The operation control module commanded the positioning systemto position the orifice of the tool at the coordinates of the startingpoint of the next toolpath, and commanded the tool and deposition deviceto deposit material along the path as before, only using the parametersfrom the materials/tools/substrates database for this tool and thismaterial.

This same set of operations was continued by the system for each path inthe manufacturing plan, requesting that the user change the tool and/ormaterial cartridge according to the labels of the paths.

After the deposition of the anode terminal, fabrication of the hollowcylindrical wall of the casing with the fusible material deposition tooland ABS material was alternated with fabrication of the other parts ofthe battery using the cartridge holding tool and the appropriatematerial cartridges, progressively building upward in height. The zincanode was deposited atop the anode terminal. Then the separator, cathodecatalyst and cathode conductor were deposited. Finally the fusiblematerial deposition tool and ABS material were used to deposit thecasing lid, which completed the fabrication of the functional zinc-airbattery.

The finished battery measured approximately 50 mm in diameter by 10 mmhigh, produced more than 1.4 V open-circuit, and was able to produceenough power (approximately 30 mW) to rotate a small electric motor fora few seconds.

This example demonstrates the ability of the freeform fabrication systemto fabricate complete functional articles which comprise multiple activematerials while employing a plurality of material deposition tools whichoperate by different material deposition mechanisms. In addition, thesystem fabricates these articles using a labeled geometric descriptionof the desired article and its subcomponents, and there are very fewrestrictions on the geometry of the article. This description can begenerated in a manner of minutes, permitting a continuum of articledesigns to be produced by the same system with no specialization ormodification of the system.

Although preferred embodiments have been depicted and described indetail herein, it will be apparent to those skilled in the relevant artthat various modifications, additions, substitutions, and the like canbe made without departing from the spirit of the invention and these aretherefore considered to be within the scope of the invention as definedin the claims which follow.

What is claimed:
 1. A method of fabricating a living three-dimensionalstructure, said method comprising: providing a data set representing aliving three-dimensional structure to be fabricated; providing one ormore printable compositions including a composition comprising ahydrogel comprising seeded cells; and printing the one or morecompositions onto a substrate in layers in a pattern in accordance withthe data set suitable to fabricate the living three-dimensionalstructure without the need to provide a negative template; wherein theprintable composition is capable of (i) bonding between printed layers,(ii) holding its shape against gravity, and (iii) cross-linking slowlyenough to prevent cell and material shearing during printing.